Method for enhancing smoldering of sludge with low oil content by using activated carbon

Abstract

A method for enhancing low-oil-content sludge smoldering by using activated carbon belongs to the technical field of sludge treatment, and adopts a forward smoldering method to improve the smoldering performance of the low-oil-content sludge and increase the smoldering peak temperature and the petroleum hydrocarbon removal rate by adding activated carbon, so that efficient harmless treatment of the low-oil-content sludge is realized, and the pollution of the low-oil-content sludge to the environment is reduced; the activated carbon not only has a combustion-supporting effect, but also can adsorb toxic and harmful gases such as benzene series and phenols generated in the smoldering process, and the adsorbed gases are further combusted and decomposed at high temperature, so that the types and quantity of the finally discharged toxic and harmful gases are greatly reduced, and the pollution risk to the environment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and particularly to a method for enhancing the smoldering of low oil-content sludge with activated carbon. Background Art

[0002] With the rapid development of the petroleum industry, the output of oily sludge has been continuously increasing. Although the oil content of low oil-content sludge is relatively low, due to its huge output and the presence of certain harmful substances such as petroleum hydrocarbons, if not properly treated, it will cause serious pollution to soil, water bodies and air. At present, there are many defects in the treatment technologies for low oil-content sludge. The biological treatment method is environmentally friendly, but the treatment cycle is long, the treatment efficiency is low, and it is easily restricted by environmental factors such as temperature and pH; the chemical treatment method, such as chemical oxidation, can effectively remove pollutants, but it requires a large amount of chemical agents, the treatment cost is high, and it may also cause secondary pollution; the physical treatment method, like centrifugal separation, has limited separation effect and is difficult to deeply remove petroleum hydrocarbons.

[0003] As an emerging treatment method, the smoldering technology, based on the principle of solid material smoldering, has the advantages of simple operation, low energy consumption and low cost, and shows certain potential in the treatment of oily sludge. However, the low oil-content sludge itself provides insufficient combustion heat, resulting in difficult stable maintenance of the smoldering process, low peak temperature, and poor removal effect of petroleum hydrocarbons, which greatly limits the application of the smoldering technology in the treatment of low oil-content sludge. Therefore, it is of great practical significance to develop a method that can enhance the smoldering effect of low oil-content sludge and improve the treatment efficiency. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for enhancing the smoldering of low oil-content sludge with activated carbon, which improves the smoldering performance of low oil-content sludge by adding activated carbon, increases the smoldering peak temperature and the removal rate of petroleum hydrocarbons, realizes the efficient and harmless treatment of low oil-content sludge, and reduces its pollution to the environment.

[0005] A method for enhancing the smoldering of low oil-content sludge with activated carbon, using the forward smoldering method, includes the following steps: Step 1: Use a quartz container as the smoldering reactor. Quartz has good heat insulation and high-temperature resistance properties; fill pollution-free river sand at the bottom of the smoldering reactor to form a pollution-free river sand layer, place the air diffuser at the bottom of the pollution-free river sand layer to make the air in the smoldering reactor evenly distributed, thereby forming an air supply system; set a heating device above the air diffuser in the pollution-free river sand layer; Step 2: Mix crude oil with soil and stir well. After a stable emulsion system is formed, low oil content sludge is obtained. Then, mix activated carbon with the low oil content sludge and river sand evenly to prepare oily sludge. Lay the oily sludge on a pollution-free river sand layer to form an oily sludge pollution layer, and cover it with clean river sand on top to insulate heat and reduce consumption, ensuring that the oily sludge burns out completely. Step 3: Install several identical thermocouples at different depths at the center of the oily sludge pollution layer using the direct push method to record the temperature changes during the smoldering process. The thermocouples are connected to an intelligent digital display and inspection instrument to monitor the temperature of each probe in real time, and connect it to a computer to collect data at a fixed frequency. Step 4: The heating device conducts initial heating on the smoldering of the oily sludge. When the temperature detected by the bottom thermocouple reaches 250 °C, turn on the air diffuser to introduce air. When the temperature detected by the bottom thermocouple reaches the peak and starts to decline, stop the heating of the heating device.

[0006] The activated carbon used in Step 2 is coconut shell activated carbon or columnar activated carbon, and the upper limit of the unit addition amount is set to 100 g / kg.

[0007] In Step 2, the mass ratio of the low oil content sludge to the river sand is 2:1, and the particle size of the river sand is 2–4 mm.

[0008] In Step 2, the particle size of the low oil content sludge is not greater than 4 mm, and the water content is 10%.

[0009] In Step 2, the particle size of the coconut shell activated carbon is 4-6 mm, and the particle size of the columnar activated carbon is 1.5 mm.

[0010] After turning on the air diffuser to introduce air in Step 4, keep the air flow rate at 2.78-6.8 cm / s. The size of the air flow rate and the uniformity of air distribution are the main factors affecting the self-sustaining smoldering repair of oily sludge. Oily sludge can undergo smoldering at an air flow rate of 2.78-6.8 cm / s. However, too high a flow rate will increase heat loss and affect the stability of smoldering. It has been verified that an air flow rate of 5.39 cm / s is an optimal parameter to ensure efficient smoldering.

[0011] A ventilation device is arranged above the smoldering reactor. Smoke and gas will be released during smoldering, and the ventilation device can ensure the personal safety of on-site workers.

[0012] A heat insulation layer is arranged outside the smoldering reactor to ensure the temperature inside the smoldering reactor and promote the smoldering reaction.

[0013] After turning on the air diffuser 4 to introduce air in Step 4, keep the air flow rate at 5.39 cm / s.

[0014] An air pump is used to supply oxygen to the inside of the smoldering reactor to oxidize and burn the oily sludge. In order to ensure the uniform distribution of air during the smoldering process of the oily sludge, an air diffuser is placed at the bottom of the smoldering reactor to evenly transport the air into the oily sludge, realizing the repeated combustion of the oily sludge.

[0015] Advantages of the present invention: 1. Adding activated carbon in the present invention provides additional fuel for the smoldering of low oil content sludge, increases the combustion heat release rate, and effectively increases the peak temperature of smoldering. Experiments show that after adding activated carbon, the average peak temperature of the system can reach about 700 °C, which is greatly increased compared with that without adding activated carbon, making the smoldering reaction more intense and stable.

[0016] 2. Under the action of activated carbon, the total petroleum hydrocarbon removal rate of low oil content sludge is significantly improved, reaching more than 99%. After sludge treatment, the petroleum hydrocarbon content is significantly reduced, meeting both the Daqing Oilfield sludge treatment specification of TPH ≤ 3000 mg / kg and the construction land soil screening standard of TPH ≤ 826 mg / kg, successfully realizing the harmless and efficient treatment of low oil content sludge.

[0017] 3. Activated carbon not only has a combustion-supporting effect, but also can adsorb toxic and harmful gases generated during the smoldering process, such as benzene series and phenols. These adsorbed gases are further burned and decomposed at high temperatures, greatly reducing the types and amounts of toxic and harmful gases emitted finally, and reducing the environmental pollution risk.

[0018] 4. Activated carbon has a wide source, relatively low price, and a small addition amount, resulting in low treatment costs. At the same time, this method reduces the use of chemical agents and eliminates the risk of secondary pollution, meeting both environmental protection requirements and achieving a win-win situation of economic and environmental benefits. Description of the drawings

[0019] Figure 1 It is a schematic diagram of the principle of the embodiment of the present invention.

[0020] Figure 2 It is a schematic diagram of the change of the smoldering T1-T5 temperature of sludge with an oil content of 2% over time under the condition of not adding activated carbon; Figure 3 It is a relationship diagram between the smoldering of sludge with different oil contents and the occurrence time of the peak temperature under the condition of not adding activated carbon; Figure 4 It is a relationship diagram between different contents of coconut shell activated carbon and the average peak temperature; Figure 5 It is a relationship diagram between different contents of coconut shell activated carbon and the average combustion propagation speed; Figure 6 It is a relationship diagram between different contents of coconut shell activated carbon and the average removal rate; Figure 7 Relationship diagram of coconut shell activated carbon with different contents and total petroleum hydrocarbon removal rate; Figure 8 Relationship diagram of columnar activated carbon with different contents and average peak temperature; Figure 9 Relationship diagram of columnar activated carbon with different contents and average combustion propagation speed; Figure 10 Relationship diagram of columnar activated carbon with different contents and average removal rate; Figure 11 Relationship diagram of columnar activated carbon with different contents and total petroleum hydrocarbon removal rate; Figure 12 Schematic diagram of peak temperatures reached by each probe at different distances from the heater for different contents of coconut shell activated carbon; Figure 13 Schematic diagram of peak temperatures reached by each probe at different distances from the heater for different contents of columnar activated carbon. Detailed implementation manners

[0021] Please refer to Figures 1 to 13 as shown, which is an embodiment of the present invention.

[0022] A method for enhancing smoldering of low - oil - content sludge with activated carbon, adopting the forward smoldering method, includes the following steps: Step 1: Use a cylindrical quartz simulation column with dimensions (Φ×H) of 160 mm×300 mm as the smoldering reactor 1. Quartz has good heat insulation and high - temperature resistance properties; a 10 - mm - thick thermal insulation cotton is arranged outside the smoldering reactor 1 as the thermal insulation layer 2 to ensure the temperature inside the smoldering reactor 1 and promote the smoldering reaction. Fill 20 - mm - thick pollution - free river sand at the bottom of the smoldering reactor 1 to form a pollution - free river sand layer 3. Place the air diffuser 4 at the bottom of the pollution - free river sand layer 3 to make the air in the smoldering reactor 1 evenly distributed, thus forming an air supply system; a 220 - V, 1000 - W thermal resistance coil is arranged above the air diffuser 4 in the pollution - free river sand layer 3 as the heating device 5. Step 2: Mix the crude oil with the soil and stir well. After a stable emulsion system is formed, low oil content sludge is obtained. Pretreat the low oil content sludge by natural drying to initially reduce its water content, and then crush it into particles with a particle size not greater than 4 mm. Then add water to adjust the water content to 10%, and mix it with river sand with a particle size of 2–4 mm in a mass ratio of 2:1. Then mix it with activated carbon, stir well, and prepare the oil-containing sludge. The activated carbon selected is coconut shell activated carbon with a particle size of 4–6 mm. Remove impurities and broken particles to ensure the quality and performance stability of the coconut shell activated carbon. The screened coconut shell activated carbon does not need to be subjected to special chemical treatment to avoid introducing new impurities. The unit addition amount of the coconut shell activated carbon is 60 g / kg, that is, the mass of the coconut shell activated carbon in every 1 kg of oil-containing sludge is 60 g. Lay 100 mm thick oil-containing sludge on the pollution-free river sand layer 3 to form an oil sludge pollution layer 6, and then cover it with 20 mm thick clean river sand 7 to insulate heat and reduce energy consumption, ensuring that the oil-containing sludge burns out completely. Step 3: Install five identical thermocouples 8 at different depths at the center of the oil sludge pollution layer 6 by the direct push method, that is, on the vertical center line of the pollution layer, arrange a thermocouple every 20 cm, and mark them as T1-T5 from bottom to top in sequence, which are used to record the temperature changes during the smoldering process. The thermocouple 8 uses a K-type armored thermocouple with a measurement range of 0~1100 °C. The thermocouple 8 is connected to an intelligent digital display and inspection instrument 9, directly connected to the data acquisition system, and reads and records the temperature data of each probe in real time at a frequency of once per second, and connects it to a computer 10 to collect data at a fixed frequency. Step 4: Use the thermal resistance coil of the heating device 5 to initially heat the smoldering of the oil-containing sludge. When the temperature detected by the bottommost thermocouple 8 (marked as T1) reaches 250 °C, turn on the air diffuser 4 to introduce air and keep the air flow rate at 5.39 cm / s. The size of the air flow and the uniformity of the air distribution are the main factors affecting the self-sustaining smoldering repair of oil-containing sludge. The oil-containing sludge can smolder at an air flow rate of 2.78 - 6.8 cm / s. However, too high a flow rate will increase heat loss and affect the stability of smoldering. After verification, an air flow rate of 5.39 cm / s is an optimal parameter, which can ensure efficient smoldering.

[0023] Wait until the temperature detected by the bottommost thermocouple 8 reaches the peak and starts to decline, and stop the heating of the thermal resistance coil of the heating device 5.

[0024] A ventilation device 11 is arranged above the smoldering reactor 1. Smoke and gas will be released during smoldering, and the ventilation device 11 can ensure the personal safety of on-site workers.

[0025] Experiment 1: Select oil-containing sludge with different oil contents for comparative experiments.

[0026] Prepare an oily sludge contaminated layer by mixing oily sludge with a particle size not greater than 4 mm and coarse river sand with a particle size of 2 - 4 mm evenly, with a mud-to-sand mass ratio of 2:1, adjusting the water content to 10%, and the oil content of the oily sludge being 2%, 5%, 8%, 10%, 12% and 15% respectively. Add 20 mm thick pollution-free river sand to the bottom layer of the smoldering reactor device; place the air diffuser at the bottom layer in the 20 mm pollution-free river sand layer; then place the thermal resistance coil on top of the air diffuser; fill 100 mm of oily sludge on top of the clean river sand, and then lay 20 mm thick clean river sand on the surface of the sludge layer. Install five identical K-type armored thermocouples with a diameter of 5 mm (measurement range 0 - 1100 °C) at the center of different depths of the oily sludge layer by the direct push method, place them at an interval of 20 mm for every two thermocouples, and the lowest thermocouple is 20 mm away from the bottom of the reactor, numbered T1 - T5 from bottom to top. The thermocouples are connected to an intelligent digital display inspection instrument to dynamically monitor the temperature of each probe. During the test, the resistance heating coil is used to initially heat the smoldering of the oily sludge. When the temperature detected by the bottom thermocouple (T1) reaches 250 °C, the air diffuser is turned on to introduce air; when the temperature of the T1 thermocouple reaches the peak and starts to decline, the resistance heating coil is immediately turned off to stop heating, and the air flow rate is controlled at 5.39 cm / s. The average peak temperature is determined by the average value of the peak temperatures measured by thermocouples T1 - T5. The average propagation speed is calculated by dividing the distance between adjacent thermocouples by the time difference when they reach 400 °C, 500 °C, and 600 °C. The average removal efficiency is the mass loss before and after smoldering, divided by the time interval between the first and the last thermocouple reaching the peak temperature. Under the condition of 0 g / kg of activated carbon addition, the schematic diagram of the variation of the peak temperature of T1 - T5 and time during the smoldering of the sludge with an oil content of 2% is as Figure 2 shown, and the variation of the peak temperature of the smoldering of the sludge with different oil contents with time is as Figure 3 shown.

[0027] After the repair is completed, soil samples are collected from the upper, middle and lower layers of the smoldering reactor respectively. By calculating the difference in the petroleum hydrocarbon content before and after the reaction in the soil sample and dividing it by the petroleum hydrocarbon content before the reaction, the total petroleum hydrocarbon removal rate can be obtained to evaluate the repair effect.

[0028] In Experiment 2, comparative experiments were carried out by selecting coconut shell activated carbon with different filling amounts.

[0029] Prepare an oily sludge contaminated layer. Coconut shell activated carbon with a particle size of 4 - 6 mm is respectively set at 20 g / kg, 40 g / kg, 60 g / kg, 80 g / kg, 100 g / kg and mixed evenly with oily sludge having a particle size not greater than 4 mm and coarse river sand with a particle size of 2 - 4 mm. The mud - sand mass ratio is 2:1, the moisture content is adjusted to 10%, and the oil content is 2%. Add 20 - mm - thick pollution - free river sand at the bottom layer of the smoldering reactor; in the 20 - mm pollution - free river sand layer, place the air diffuser at the bottommost layer; then place the thermal resistance coil on top of the air diffuser; fill 100 - mm - thick oily sludge on top of the clean river sand, and then lay 20 - mm - thick clean river sand on the surface of the sludge layer. Install five identical K - type armored thermocouples with a diameter of 5 mm (measurement range: 0 - 1100 °C) at the center of different depths of the oily sludge layer by the direct - push method. Place them at an interval of 20 mm between every two thermocouples. The lowest - layer thermocouple is 20 mm away from the bottom of the reactor, and label them T1 - T5 from bottom to top. The thermocouples are connected to an intelligent digital display and patrol inspection instrument to dynamically monitor the temperature of each probe. During the experiment, the resistance heating coil conducts initial heating on the smoldering of the oily sludge. When the temperature detected by the bottom thermocouple (T1) reaches 250 °C, turn on the air diffuser to introduce air; when the temperature of the T1 thermocouple reaches the peak value and starts to decline, immediately turn off the resistance heating coil to stop heating, and control the air flow rate at 5.39 cm / s. The average peak temperature is determined by the average value of the peak temperatures measured by thermocouples T1 - T5. The average propagation speed is calculated by dividing the distance between adjacent thermocouples by the time difference when they reach 400 °C, 500 °C, and 600 °C. The average removal efficiency is the mass loss before and after smoldering, divided by the time interval between the first and the last thermocouple reaching the peak temperature. When the oil content in the sludge is certain, the relationship between different contents of coconut shell activated carbon and the average peak temperature is as shown in Figure 4 shown, the relationship with the average combustion propagation speed is as shown in Figure 5 shown, the relationship with the average removal rate is as shown in Figure 6 shown, and the change in the peak temperature reached by each probe at different distances from the heater is as shown in Figure 12 shown.

[0030] After the repair is completed, collect soil samples from the upper, middle, and lower layers of the smoldering reactor respectively. By calculating the difference in the petroleum hydrocarbon content before and after the reaction in the soil sample and dividing it by the petroleum hydrocarbon content before the reaction, the total petroleum hydrocarbon removal rate can be obtained to evaluate the repair effect. The relationship between the addition amount of coconut shell activated carbon and the total petroleum hydrocarbon removal rate is as shown in Figure 7 shown.

[0031] Experiment three: Conduct a comparative experiment by selecting columnar activated carbon with different filling amounts.

[0032] Prepare an oily sludge contaminated layer by mixing columnar activated carbon with a particle size of 1.5 mm at 20 g / kg, 40 g / kg, 60 g / kg, 80 g / kg, 100 g / kg respectively with oily sludge having a particle size not greater than 4 mm and coarse river sand with a particle size of 2 - 4 mm evenly. The mud - sand mass ratio is 2:1, adjust the moisture content to 10% and the oil content to 2%. Add 20 - mm - thick pollution - free river sand at the bottom layer of the smoldering reactor device; in the 20 - mm pollution - free river sand layer, place the air diffuser at the bottommost layer; then place the thermal resistance coil on top of the air diffuser; fill 100 - mm oily sludge on top of the clean river sand, and then lay a 20 - mm - thick clean river sand layer on the surface of the sludge layer. Install the same K - type armored thermocouple with a diameter of 5 mm (measurement range 0 - 1100 °C) at the center of different depths of the oily sludge layer by the direct - push method. Place every two thermocouples at an interval of 20 mm, and the lowest - layer thermocouple is 20 mm away from the bottom of the reactor, numbered T1 - T5 from bottom to top. The thermocouples are connected to an intelligent digital display and inspection instrument to dynamically monitor the temperature of each probe. During the experiment, the resistance heating coil is used to initially heat the smoldering of the oily sludge. When the temperature detected by the bottom thermocouple (T1) reaches 250 °C, turn on the air diffuser to introduce air; when the temperature of the T1 thermocouple reaches the peak value and starts to decline, immediately turn off the resistance heating coil to stop heating, and control the air flow rate at 5.39 cm / s. The average peak temperature is determined by the average value of the peak temperatures measured by thermocouples T1 - T5. The average propagation speed is calculated by dividing the distance between adjacent thermocouples by the time difference when they reach 400 °C, 500 °C, and 600 °C. The average removal efficiency is the mass loss before and after smoldering, divided by the time interval between the first and the last thermocouple reaching the peak temperature. When the oil content in the sludge is certain, the relationship between different contents of columnar activated carbon and the average peak temperature is as Figure 8 shown, the relationship with the average combustion propagation speed is as Figure 9 shown, the relationship with the average removal rate is as Figure 10 shown, and the peak temperatures reached by each probe at different distances from the heater are as Figure 13 shown.

[0033] After the repair is completed, collect soil samples from the upper, middle, and lower layers of the smoldering reactor respectively. By calculating the difference in the petroleum hydrocarbon content before and after the reaction in the soil sample and dividing it by the petroleum hydrocarbon content before the reaction, the total petroleum hydrocarbon removal rate can be obtained to evaluate the repair effect. The relationship between the addition amount of columnar activated carbon and the total petroleum hydrocarbon removal rate is as Figure 11 shown.

[0034] Table 1 Sources and Main Physical and Chemical Properties of Crude Oil Source Daqing City, Heilongjiang Province Sulfur content (w%) < 0.2 Viscosity mPa.s (50 °C) 23.79 Nitrogen content (w%) < 0.3 <![CDATA[Density g / cm 3 (at 20°C)]]> 0.8604 Nickel content (w%) 2.3 Freezing point (°C) 23 Vanadium content (w%) 0.08 Residual carbon (w%) 3.1 Wax content (w%) 25.2 From Figure 2It can be seen that without the participation of activated carbon, when the oil content of the oily sludge is less than 5%, after the thermocouple T1 reaches the peak temperature and the heater is turned off, the temperatures measured by T1 - T5 decrease successively, indicating that the heat generated by the bottom sludge cannot support the continuous upward movement of the smoldering front. After detection, the petroleum hydrocarbon removal rate of the treated soil sample fails to meet the oily sludge treatment standard, and the oily sludge residue is mostly black, showing that a large amount of crude oil still remains, confirming that the sludge with an oil content lower than 5% is difficult to maintain the smoldering reaction.

[0035] As can be seen from Figure 3 It can be seen that when the oil content of the oily sludge is between 5% and 15%, the peak temperature of its combustion varies between 415 °C and 480 °C, an increase of 13.5%, and the time when the peak appears also shortens from 135 min to 90 min, a decrease of 33%. The experiment shows that within a certain range, an increase in the oil content of the oily sludge will cause the average peak temperature of its combustion to rise. As the oil content increases, more fuel participates in combustion per unit time, the heat release rate of the sludge per unit volume increases, and the heat generated increases accordingly, resulting in an increase in the peak temperature. However, when the oil content increases to 12%, the rising trend of the peak temperature slows down. This is because smoldering is restricted by oxygen supply. At a constant air flow rate, the higher the oil content, the greater the amount of air consumed by the sludge per unit volume. When the air supply reaches the saturation state, the average peak temperature tends to be stable.

[0036] As can be seen from Figures 4 to 11 It can be seen that adding activated carbon of different types and contents to the device enables the oily sludge with an oil content of 2% to undergo smoldering combustion.

[0037] As can be seen from Figure 4 and Figure 8 It can be seen that with the increase in the content of activated carbon, the average peak temperatures in the coconut shell activated carbon and columnar activated carbon systems both increase. The coconut shell activated carbon increases from 468 °C to 693 °C, and the columnar activated carbon increases from 487 °C to 753 °C. This is because the activated carbon acts as fuel, promoting the heat release rate of the oily sludge per unit volume to increase within the same time, and the amount of heat released also increases accordingly, resulting in an increase in the peak temperature. However, throughout the process, the air flow rate remains constant at 5.39 cm / s. When activated carbon is added, the air consumption per unit volume of the oily sludge increases. Due to the limited air supply, the reaction rate decreases. As the reaction progresses, until the air required by the oily sludge reaches the saturation state, the average peak temperature will tend to be stable.

[0038] Similarly, as can be seen from Figure 5 , Figure 6 , Figure 9 and Figure 10It can be seen that the average combustion propagation speed and the average removal rate show a downward trend with the increase in the activated carbon content. The rate of decrease gradually slows down and then tends to a stable state.

[0039] It can be seen from Figure 7 and Figure 11 that when the addition amounts of coconut shell activated carbon and columnar activated carbon are both 20 g / kg, the removal rate of total petroleum hydrocarbons is generally around 98%. Compared with the situation where the removal rate of total petroleum hydrocarbons exceeds 99% when the addition amount is between 40 - 100 g / kg, the treatment effect at this time is relatively poor. However, after the smoldering of oily sludge with an oil content of 2% after adding 20 g / kg of coconut shell activated carbon, the petroleum hydrocarbon content in the residue of the oily sludge is 550 mg / kg; after adding 20 g / kg of columnar activated carbon and the smoldering of oily sludge with an oil content of 2%, the petroleum hydrocarbon content in the residue of the oily sludge is 450 mg / kg. Both meet the relevant requirements (TPH ≤ 3000 mg / kg) for treating oil sludge in Daqing Oilfield and comply with the limit requirements of the soil screening values for construction land (TPH ≤ 826 mg / kg).

[0040] It can be seen from Figures 8 to 12 that in the coconut shell activated carbon and columnar activated carbon systems, with the increase in the activated carbon content, the peak temperatures measured by T1 - T5 thermocouples all gradually increase, and when the activated carbon content reaches 100 g / kg, the peak temperature reaches the highest value. In addition, the farther the distance between the thermocouple and the heating device, the lower the measured peak temperature. This is because the temperature of the thermocouple is significantly affected by the heater. The closer it is to the heater, the greater the influence and the higher the temperature; as the distance between the thermocouple and the heater increases, the loss of heat during the transfer process increases, resulting in a decrease in the peak temperature.

[0041] Through the comparative analysis of the effects of coconut shell activated carbon and columnar activated carbon on the smoldering of oily sludge with a low oil content, the results show that after adding columnar activated carbon, indicators such as the average peak temperature, average combustion propagation speed, and average removal rate of the sludge are all better than those after adding coconut shell activated carbon, and the petroleum hydrocarbon content in the residue of the oily sludge is lower. This fully shows that the treatment effect of columnar activated carbon is better when treating oily sludge with a low oil content. It also confirms that in the smoldering technology, using activated carbon as a combustion aid for strengthening the remediation of soil polluted by oily sludge with a low oil content is feasible. The injection of activated carbon provides an efficient and environmentally friendly solution for the smoldering remediation of sites polluted by oily sludge with a low oil content (< 5%) and has broad application prospects.

Claims

1. A method for enhancing the smoldering of low oil-content sludge by activated carbon, characterized in that, It includes the following steps: Step 1: Use a quartz container as the smoldering reactor (1). Fill the bottom of the smoldering reactor (1) with pollution-free river sand to form a pollution-free river sand layer (3). Place the air diffuser (4) at the bottom of the pollution-free river sand layer (3) to evenly distribute the air in the smoldering reactor (1), thereby forming an air supply system. Set a heating device (5) above the air diffuser (4) in the pollution-free river sand layer (3). A ventilation device (11) is provided above the smoldering reactor (1). Step 2: Mix crude oil and soil and stir well. After forming a stable emulsion system, obtain low oil content sludge. Then mix activated carbon, low oil content sludge, and river sand evenly to prepare oily sludge. Lay the oily sludge on the pollution-free river sand layer (3) to form an oily sludge pollution layer (6), and then cover it with clean river sand (7). Step 3: Install several identical thermocouples (8) at different depths at the center of the oily sludge pollution layer (6) using the direct push method to record the temperature change during the smoldering process. The thermocouple (8) is connected to an intelligent digital display and inspection instrument (9) to monitor the temperature of each probe in real time and connect it to a computer (10) to collect data at a fixed frequency. Step 4: The heating device (5) conducts initial heating on the smoldering of the oily sludge. When the temperature detected by the bottom thermocouple (8) reaches 250 °C, turn on the air diffuser (4) to introduce air. When the temperature detected by the bottom thermocouple (8) reaches the peak and starts to decline, stop the heating of the heating device (5).

2. The method for enhancing the smoldering of low oil-content sludge by activated carbon according to claim 1, wherein: The activated carbon used in Step 2 is coconut shell activated carbon or columnar activated carbon, and the upper limit of the unit addition amount is set to 100 g / kg.

3. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 1, characterized in that: In Step 2, the mass ratio of the low oil content sludge to the river sand is 2:1, and the particle size of the river sand is 2–4 mm.

4. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 1, characterized in that: In Step 2, the particle size of the low oil content sludge is not greater than 4 mm, and the water content is 10%.

5. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 2, characterized in that: In Step 2, the particle size of the coconut shell activated carbon is 4-6 mm, and the particle size of the columnar activated carbon is 1.5 mm.

6. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 1, characterized in that: In Step 4, after turning on the air diffuser (4) to introduce air, keep the air flow rate at 2.78 - 6.8 cm / s.

7. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 1, characterized in that: A ventilation device (11) is provided above the smoldering reactor (1).

8. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 1, characterized in that: A heat preservation layer (2) is provided outside the smoldering reactor (1).

9. A method for enhancing the smoldering of low oil content sludge with activated carbon according to claim 6, characterized in that: In Step 4, after turning on the air diffuser (4) to introduce air, keep the air flow rate at 5.39 cm / s.

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