Thermal desorption system and method for treating high-concentration mercury and petroleum hydrocarbon combined polluted soil

Abstract

The invention discloses a thermal desorption system and method for treating high-concentration mercury and petroleum hydrocarbon combined polluted soil, indirect thermal desorption equipment comprises an upper-layer furnace kiln, a lower-layer furnace kiln and an air pre-heater, a natural gas burner and a plurality of burners are arranged below the lower-layer furnace kiln, a thermal desorption chamber and a lower-layer flue gas jacket are arranged in the lower-layer furnace kiln, and a lower-layer flue gas jacket is arranged in the lower-layer furnace kiln. A thermal desorption chamber is arranged in the upper-layer kiln, a lower-layer flue gas jacket is arranged around the thermal desorption chamber, a drying chamber and an upper-layer flue gas jacket are arranged in the upper-layer kiln, the upper-layer flue gas jacket is arranged around the drying chamber, and the lower-layer flue gas jacket is communicated with the upper-layer flue gas jacket; high-temperature flue gas in the upper-layer flue gas jacket enters an air pre-heater to pre-heat air, and the pre-heated air is conveyed to a natural gas burner; the indirect thermal desorption system is adopted for repairing the high-concentration mercury and petroleum hydrocarbon (C10-C40) combined polluted soil, the tail gas treatment system (dust removal, condensation, gas-liquid separation, adsorption, washing unit and adsorption) and the wastewater treatment system are combined to achieve up-to-standard discharge of tail gas and wastewater, and the treatment energy consumption is remarkably reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and in particular relates to a thermal desorption system and method for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons. Background Art

[0002] Mercury is a silvery-white liquid metal that evaporates at room temperature. As a persistent, bioaccumulative and neurotoxic pollutant, it has always attracted widespread attention. Mercury mainly exists in the form of inorganic mercury, organic mercury and elemental mercury. Inorganic mercury and organic mercury are commonly found in contaminated water sources and food chains, and are toxic to the human body through ingestion of food and water. Petroleum hydrocarbons (C 10 -C 40 Petroleum hydrocarbons are a mixture of hydrocarbons with 10 to 40 carbon atoms and are among the longer carbon-chain components of petroleum. Petroleum hydrocarbons are hydrophobic and difficult to biodegrade. Once in the soil, they are difficult to quickly remove and remain in the soil and groundwater for a long time, entering the human body through the food chain and causing harm to human health.

[0003] With the implementation of the "withdraw from secondary and enter tertiary" and "withdraw from urban areas and enter industrial parks" projects, old factories have moved out of urban areas, leaving behind a large number of abandoned sites. Due to the historical production of the factories, the soil of the abandoned sites may be polluted by mercury and petroleum hydrocarbons, posing a potential hazard to the environment and human health. Commonly used remediation technologies for mercury-contaminated soil include thermal desorption remediation technology, solidification and stabilization remediation technology, and leaching remediation technology. Petroleum hydrocarbons (C 10 -C 40 ) Commonly used remediation technologies for contaminated soil include thermal desorption remediation technology, chemical oxidation remediation technology and biological remediation technology. Thermal desorption technology is a method for treating mercury and petroleum hydrocarbons (C 10 -C 40 ) is one of the main technologies for contaminating soil. It uses direct or indirect heating to heat the contaminated soil to a certain temperature for a period of time, and eventually the mercury and petroleum hydrocarbons (C 10 -C 40 ) evaporates and separates from the soil. 10 -C 40 There are many studies on thermal desorption remediation of contaminated soil, but there are technical problems such as high energy consumption of equipment. 10 -C 40 ) There are few studies on thermal desorption remediation of complex contaminated soils, and complex pollution places higher demands on the thermal desorption remediation system. At the same time, the mixed gas discharged by the thermal desorption equipment has more complex components, containing mercury, petroleum hydrocarbons and dust particles, which need to be efficiently treated to avoid pollution to the external environment. Summary of the Invention

[0004] Aiming at the current pollution problem of coexistence of high concentration mercury and petroleum hydrocarbons in soil, there are problems such as difficulty in soil remediation and tail gas treatment during thermal desorption treatment, high energy consumption of equipment, etc., the present invention provides a thermal desorption system and method for treating soil contaminated with high concentration mercury and petroleum hydrocarbons. The indirect thermal desorption system is used to treat high concentration mercury and petroleum hydrocarbons (C 10 -C 40 ) Complex contaminated soil is repaired, and the tail gas treatment system and wastewater treatment system are combined to achieve standard discharge of tail gas and wastewater.

[0005] The present invention adopts the following technical solutions:

[0006] On the one hand, the present invention provides a thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons, comprising a pretreatment device, an indirect thermal desorption device, an exhaust gas treatment device, and a wastewater treatment device. The indirect thermal desorption device comprises an upper furnace, a lower furnace, and an air preheater. The lower furnace and the upper furnace are both screw-propelled. A natural gas burner and a plurality of burners are disposed below the lower furnace. The lower furnace is provided with a thermal desorption chamber and a lower flue gas jacket, the lower flue gas jacket being disposed around the thermal desorption chamber. The upper furnace is provided with a drying chamber and an upper flue gas jacket, the upper flue gas jacket being disposed around the drying chamber, and the lower flue gas jacket and the upper flue gas jacket being connected. The high-temperature flue gas in the upper flue gas jacket enters the air preheater to preheat the air, and the preheated air is transported to the natural gas burner.

[0007] The contaminated soil to be treated passes through the drying chamber and the thermal desorption chamber in sequence. The high-temperature flue gas generated by the combustion of the natural gas burner enters the lower flue gas jacket and the upper flue gas jacket in sequence, and heats the contaminated soil in the thermal desorption chamber and the drying chamber at high temperature. The water vapor, mercury gas and organic gas evaporated from the drying chamber and the thermal desorption chamber are transported to the exhaust gas treatment equipment for treatment. The waste liquid generated in the process of treating the exhaust gas by the exhaust gas treatment equipment enters the wastewater treatment equipment for treatment.

[0008] Preferably, the natural gas burner generates high-temperature flue gas of 800-1200° C., and the contaminated soil is heated to 450-550° C. in the thermal desorption chamber for a residence time of 15-20 minutes.

[0009] Preferably, the tail gas treatment equipment includes:

[0010] The dust removal unit separates the dust particles in the thermal desorption exhaust gas from the dust-containing airflow;

[0011] A condensation unit, wherein the temperature of the thermal desorption tail gas after being treated by the dust removal unit is suddenly reduced by the condensation unit, water vapor, mercury gas and organic matter gas in the thermal desorption tail gas are condensed, and the condensate is input into the wastewater treatment equipment for treatment;

[0012] The gas-liquid separator I performs gas-liquid separation on the condensed tail gas and inputs the separated waste liquid into the wastewater treatment equipment for treatment;

[0013] Adsorption unit I, using a two-stage activated carbon adsorption process, removes pollutants by subjecting the tail gas separated by the gas-liquid separator I to adsorption treatment on sulfur-loaded and mercury-removing activated carbon;

[0014] The washing unit collects the tail gas discharged from the adsorption unit I and performs an oxidation reaction under acidic conditions to convert the mercury-containing substances in the tail gas from gaseous state to dissolved state, and the petroleum hydrocarbons (C 10 -C 40 ) is oxidized and degraded, and the generated waste liquid is input into the wastewater treatment equipment;

[0015] Gas-liquid separator II, which performs gas-liquid separation on the tail gas treated by the washing unit, and the resulting waste liquid is input into the wastewater treatment equipment;

[0016] Adsorption unit II, the tail gas separated by the gas-liquid separator II is subjected to sulfur-loaded mercury-removing activated carbon adsorption treatment to eliminate the residual mercury and petroleum hydrocarbons (C 10 -C 40 ) and smoke.

[0017] Preferably, the wastewater treatment equipment comprises:

[0018] A regulating tank for collecting waste liquid generated by the tail gas treatment equipment and regulating water quality and quantity;

[0019] Oxidation tank, adjust the pH value of the wastewater, add oxidant to carry out oxidation reaction so that the mercury pollutants in the wastewater exist in ionic form, and convert the contained petroleum hydrocarbons (C 10 -C 40 ) oxidative decomposition into CO2 and H2O;

[0020] A neutralization flocculation sedimentation tank is used to collect the supernatant of the oxidation tank and use a flocculant to form mercury sulfide precipitation and hydroxide flocs to precipitate the pollutants;

[0021] The activated carbon filter collects the supernatant of the neutralization flocculation sedimentation tank, and adsorbs pollutants in the supernatant through the activated carbon filter, and the wastewater after adsorption and filtration meets the discharge standards.

[0022] Further preferably, the pretreatment equipment includes: crushing and screening equipment, moisture content regulating equipment and conveying equipment in sequence. The crushing and screening equipment crushes the excavated contaminated soil, cleans the large-particle slag with a diameter exceeding 30 mm screened out with high-pressure water flow, and delivers the soil particles with a diameter less than 30 mm screened out to the indirect thermal desorption equipment through the conveying equipment.

[0023] On the other hand, the present invention also provides a thermal desorption method for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons, using the above-mentioned thermal desorption system, the method comprising the following steps:

[0024] Step 1: crush and screen the excavated contaminated soil, and input the soil with a set particle size into the indirect thermal desorption equipment;

[0025] Step 2: The contaminated soil enters the drying chamber of the upper kiln for preheating and then enters the thermal desorption chamber of the lower kiln for high-temperature heating. Water vapor, mercury gas, and organic matter gas are generated in the drying chamber and the thermal desorption chamber.

[0026] Step 3: The tail gas treatment equipment collects water vapor, mercury gas, and organic matter gas generated by the contaminated soil, and passes them through the dust removal unit + condensation unit + gas-liquid separator I + adsorption unit I + washing unit + gas-liquid separator II + adsorption unit II in sequence to remove residual pollutants in the tail gas;

[0027] Step 4: The wastewater treatment equipment collects the waste liquid generated during the treatment process of the tail gas treatment equipment, and uses chemical oxidation + neutralization flocculation precipitation + activated carbon adsorption to treat it to meet the standards, and then discharges it through the pipe.

[0028] Preferably, in step 3, the condensation unit condenses the gas after dust removal by a sudden temperature drop method, and the condensed tail gas enters the gas-liquid separator I; the gas obtained after treatment in the gas-liquid separator I enters the adsorption unit I, and is filtered and purified by a two-stage series sulfur-loaded and mercury-removing activated carbon adsorption; the purified tail gas enters the washing unit, and an oxidation reaction occurs under acidic conditions to convert the remaining mercury-containing substances in the tail gas from gas to dissolved state, and the petroleum hydrocarbons (C 10 -C 40 ) is oxidized and degraded; the gas treated by the washing unit is then passed through the gas-liquid separator II to remove water vapor, and the remaining tail gas is then adsorbed by the sulfur-loaded mercury-removing activated carbon in the adsorption unit II to remove residual pollutants.

[0029] Further preferably, in step 3, a cyclone dust collector and a bag dust collector are sequentially used in the dust removal unit to remove dust from the thermal desorption tail gas.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] A. The thermal desorption system and method provided by the present invention adopts an indirect thermal desorption device with an upper furnace, a lower furnace and a natural gas burner. The high-temperature flue gas generated by the combustion of the natural gas burner is transported in the lower flue gas jacket and the upper flue gas jacket, and indirectly heats the thermal desorption chamber and the drying chamber from bottom to top. The contaminated soil to be treated is first preheated in the upper furnace, and then enters the lower furnace to receive high-temperature heating. After treatment, the petroleum hydrocarbons (C 10 -C 40 ) and mercury concentrations were 178.2 mg / kg and 4.6 mg / kg, respectively, with removal rates of 93.2% and 95.1%, respectively, both meeting the remediation target value requirements and reducing energy consumption.

[0032] B. This invention treats thermal desorption tail gas evaporated from contaminated soil by sequentially utilizing a "dust removal unit + condensation unit + gas-liquid separator I + adsorption unit I + scrubbing unit + gas-liquid separator II + adsorption unit II" process. The tail gas is then discharged through a 15-meter-high exhaust stack. The emission concentrations and rates of mercury, non-methane hydrocarbons, and particulate matter in the exhaust gas meet the second period standard requirements of the "Emission Limits of Air Pollutants" (DB44 / 27-2001).

[0033] C. The present invention adopts a condensation unit with a sudden temperature drop method in the tail gas treatment equipment, and also sends the tail gas discharged from the adsorption unit I into the washing unit, where an oxidation reaction occurs under acidic conditions, so that the mercury-containing substances in the tail gas are converted from gaseous state to dissolved state, and the petroleum hydrocarbons (C 10 -C 40 ) are oxidized and degraded, further improving the treatment efficiency of pollutants in the exhaust gas, and the waste liquid generated in the exhaust gas treatment process is uniformly treated. After being treated in the "regulating tank + oxidation tank + neutralization flocculation sedimentation tank + activated carbon filter" and other links, the concentrations of mercury and petroleum hydrocarbons in the wastewater meet the emission concentration requirements of the "Water Pollutant Emission Limits" (DB44 / 26-2001) and other standards.

[0034] D. The present invention is to treat high concentration mercury and petroleum hydrocarbons (C 10 -C 40 ) Composite contaminated soil thermal desorption remediation and corresponding tail gas and wastewater treatment, after the treatment is completed, the soil, waste gas and wastewater all reach the corresponding standard values, meet the remediation requirements of contaminated soil and meet the requirements of secondary pollution environment management of atmosphere and wastewater. The provided thermal desorption system uses high-temperature flue gas to indirectly heat the contaminated soil and preheat the combustion air to achieve waste heat recovery. It has been verified that the indirect thermal desorption equipment of the present invention is used to treat contaminated soil, and the gas energy consumption is 20 to 30m 3 / t, compared with the energy consumption of 35-50m3 / t for treating contaminated soil by conventional thermal desorption equipment on the market. 3 / t, the energy consumption of thermal desorption treatment is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present invention, the following will briefly introduce the drawings required for use in the specific embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0036] Figure 1 This is a flow chart of the indirect thermal desorption treatment of contaminated soil provided by the present invention;

[0037] Figure 2 This is a schematic structural diagram of the indirect thermal desorption equipment provided by the present invention;

[0038] Figure 3 This is a processing flow chart of the tail gas treatment equipment provided by the present invention;

[0039] Figure 4 It is a processing flow chart of the wastewater treatment equipment provided by the present invention.

[0040] The following are marked in the figure:

[0041] 1-Upper furnace, 11-Upper flue gas jacket, 12-Drying chamber; 2-Lower furnace, 21-Lower flue gas jacket, 22-Thermal desorption chamber; 3-Natural gas burner; 4-Burner; 5-Air preheater; 6-Blower; 7-Feed hopper; 8-Feed air lock; 9-Discharge air lock; 10-High-temperature flue gas. DETAILED DESCRIPTION

[0042] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0045] like Figure 1 and Figure 2 As shown, the present invention provides a thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons, including a pretreatment device, an indirect thermal desorption device, an exhaust gas treatment device, and a wastewater treatment device. The pretreatment device includes a crushing and screening device, a moisture content adjustment device, and a conveying device in sequence. The crushing and screening device crushes the excavated contaminated soil, cleans the large particles of slag exceeding 30 mm with high-pressure water flow, and transports the soil particles less than 30 mm that are screened to the indirect thermal desorption device via the conveying device.

[0046] The indirect thermal desorption equipment includes an upper furnace 1, a lower furnace 2, a feed hopper 7, an air preheater 5, a blower 6, a feed air lock 8 and a discharge air lock 9. The lower furnace 2 and the upper furnace 1 are both spiral propulsion type. A natural gas burner 3 and several burners 4 are arranged below the lower furnace 2. A thermal desorption chamber 22 and a lower flue gas jacket 21 are provided in the lower furnace 2. The lower flue gas jacket 21 is arranged around the thermal desorption chamber 22, and the spiral propulsion shaft is located in the thermal desorption chamber 22. The upper furnace 1 is provided with a drying chamber 12 and an upper flue gas jacket 11. The upper flue gas jacket 11 is arranged around the drying chamber 12. The spiral propulsion shaft is located in the drying chamber 12, and the lower flue gas jacket 21 is connected to the upper flue gas jacket 11; the high-temperature flue gas in the upper flue gas jacket 11 enters the air preheater 5 to preheat the air, and the preheated air is transported to the natural gas burner 3; the material enters the feed hopper 7, and then enters the drying chamber 12 in the upper furnace 1. Under the action of the spiral propulsion, the material is gradually pushed from one end of the upper furnace 1 to the other end, and enters the thermal desorption chamber 22 in the lower furnace 2 from the lower outlet. Under the action of the spiral propulsion inside the lower furnace 2, the material is pushed from one end to the other end and output.

[0047] The contaminated soil to be treated passes through the drying chamber 12 and the thermal desorption chamber 22 in sequence. The combustion of the natural gas burner 3 will generate high-temperature flue gas at 800-1200°C, which first enters the lower flue gas jacket 21. The flue gas heats the wall of the lower furnace 2 in the lower flue gas jacket 21, thereby indirectly heating the material. The contaminated soil is heated to 450-550°C in the thermal desorption chamber 22 for 15-20 minutes. The high-temperature flue gas continues to ascend and enter the upper flue gas jacket 11, heating the wall of the upper furnace 1 and indirectly heating the material entering the upper furnace 1, thereby heating the contaminated soil in the thermal desorption chamber 22 and the drying chamber 12. At the same time, the blower 6 injects air into the air preheater 5, and the rising high-temperature flue gas 10 further heats the air preheater 5 to obtain preheated air, and the preheated air then enters the natural gas burner 3 as a combustion-supporting gas; the water vapor, mercury gas and organic gas evaporated from the drying chamber 12 and the thermal desorption chamber 22 are transported to the exhaust gas treatment equipment for treatment, and the waste liquid generated in the process of exhaust gas treatment by the exhaust gas treatment equipment enters the wastewater treatment equipment for treatment.

[0048] In the thermal desorption chamber 22, the mercury and petroleum hydrocarbons (C 10 -C 40 The pollutants are heated to boiling point and separated as a gas. The soil after thermal desorption is transported to the discharge silo via a scraper conveyor. A humidifier is installed at the thermal desorption outlet to humidify the discharged soil, controlling its moisture content and preventing the generation of excessive water vapor due to excessive soil temperature. After leaving the upper flue gas jacket 11, the flue gas enters the air preheater 5 to preheat the combustion air used by the burner group, thereby recovering waste heat.

[0049] like Figure 3 As shown, the tail gas treatment equipment includes: dust removal unit, condensation unit, gas-liquid separator I, adsorption unit I, washing unit, gas-liquid separator II and adsorption unit II. The functions of each unit are as follows: the dust removal unit separates the dust particles in the thermal desorption tail gas from the dust-containing air flow; the thermal desorption tail gas treated by the dust removal unit is subjected to a sudden temperature drop by the condensation unit to condense the water vapor, mercury gas and organic matter gas in the thermal desorption tail gas into liquid. The condensation unit can remove more than 90% of mercury in the tail gas; the tail gas after condensation by the gas-liquid separator I has a high moisture content and is subjected to gas-liquid separation treatment , the separated waste liquid is input into the wastewater treatment equipment for treatment; the adsorption unit I adopts a secondary activated carbon adsorption process, and the tail gas separated by the gas-liquid separator I is adsorbed on the sulfur-loaded mercury-removing activated carbon to remove pollutants. The sulfur-loaded mercury-removing activated carbon used is based on activated carbon and added with elemental sulfur that has a strong affinity with mercury. It has a developed internal pore structure, a large specific surface area, a strong adsorption capacity, and a high adsorption efficiency for mercury; the washing unit receives the tail gas discharged by the adsorption unit I, and an oxidation reaction occurs under acidic conditions, so that the mercury-containing substances in the tail gas are converted from gaseous to dissolved state, and the petroleum hydrocarbons (C10 -C 40 ) is oxidized and degraded into CO2 and H2O, thereby achieving the purpose of purification, and the generated waste liquid is input to the wastewater treatment equipment; the gas-liquid separator II further separates the tail gas treated by the washing unit through gas-liquid separation, and the resulting waste liquid is input to the wastewater treatment equipment; the adsorption unit II conducts sulfur-loaded mercury-removing activated carbon adsorption treatment on the tail gas separated by the gas-liquid separator II to eliminate the residual mercury and petroleum hydrocarbons (C 10 -C 40 ) and smoke.

[0050] like Figure 4 As shown in the figure, the wastewater treatment equipment includes: regulating tank, oxidation tank, neutralization flocculation sedimentation tank and activated carbon filter. The regulating tank collects the waste liquid generated by the tail gas treatment equipment and adjusts the water quality and quantity; the oxidation tank adjusts the pH value of the wastewater. By adding oxidants to the oxidation tank to react with pollutants to produce Fenton oxidation reaction, the mercury pollutants in the wastewater are oxidized and exist in the form of ions, and the petroleum hydrocarbons (C 10 -C 40 ) is oxidized and degraded into CO2 and H2O; the neutralization flocculation sedimentation tank collects the supernatant of the oxidation tank, and uses flocculants (alkali, sodium sulfide, PFS+PAC, PAM, etc.) to form mercury sulfide precipitation and hydroxide floccules to precipitate the pollutants; the activated carbon filter collects the supernatant of the neutralization flocculation sedimentation tank, and adsorbs the pollutants in the supernatant, and the wastewater after adsorption and filtration meets the discharge standards. The neutralization flocculation sedimentation tank adopted in the present invention is preferably set up in two stages. The sludge produced by flocculation and precipitation enters the sludge concentration tank, and is filtered by a plate and frame filter press to obtain a mud cake and a filtrate, and the filtrate is returned to the regulating tank for treatment. Of course, if the water quality is still unqualified after filtration by the activated carbon filter, it will be returned to the regulating tank for further treatment until it meets the discharge standards.

[0051] Example

[0052] Taking a contaminated site in South China as an example, the present invention uses the system and method of the present invention to treat soil contaminated with high concentrations of mercury and petroleum hydrocarbons.

[0053] The site was previously used for electrical plant production, cable processing, and fluorescent lamp production. According to the results of the site environmental survey and risk assessment, there are mercury and petroleum hydrocarbons (C 10 -C 40 ) Composite contaminated soil, contaminated area is 771m 2 , the depth is 0~1m, and the pollution volume is 771m 3 , petroleum hydrocarbons (C 10 -C 40) exceeded the standard concentration by 2620 mg / kg, and the mercury exceeded the standard concentration by 94.8 mg / kg. Mercury speciation analysis revealed that the mercury in the contaminated soil is primarily in the form of inorganic mercury, accounting for approximately 95.4%, organic mercury for 3.4%, and elemental mercury for 1.2%. According to the geological survey report, the soil layers at the site are divided into plain fill, clay, and fine sand from top to bottom. The contaminated soil layer is primarily plain fill, with colors ranging from reddish-brown, gray-black, gray-brown, reddish-brown, light gray, and black. It is primarily composed of silt and clay, is slightly damp, and has a loose structure, with localized sandy clay and a small amount of gravel.

[0054] Table 1 Target values ​​and engineering quantities for site soil contaminant remediation

[0055]

[0056] According to the actual pollution situation of the site and the results of risk assessment, mercury and petroleum hydrocarbons (C 10 -C 40 ) concentration exceeds the standard and the risk to human health exceeds the acceptable risk level. The contaminated soil in the area needs to be remediated. The specific steps are as follows:

[0057] (1) Pretreatment of contaminated soil

[0058] The excavated contaminated soil is crushed and screened, and large particles larger than 30 mm are used as slag and cleaned with high-pressure water. Soil particles smaller than 30 mm are conveyed to the indirect thermal desorption equipment through a conveying device.

[0059] (2) Thermal desorption remediation of contaminated soil

[0060] The pre-treated contaminated soil material is preheated and dried in the upper kiln drying chamber, and the water contained in it evaporates. The preheated and dried material enters the thermal desorption chamber of the lower kiln and is heated to 450-550℃ for 15-20 minutes. The mercury and petroleum hydrocarbons (C 10 -C 40 ) is heated to boiling point and separated in the form of gas. The soil after thermal desorption heat treatment is conveyed to the discharge bin by a scraper conveyor. A humidifier is installed at the thermal desorption discharge port to humidify the discharged soil and control the moisture content of the soil to about 10%, so as to avoid the phenomenon of generating a large amount of water vapor due to excessively high soil temperature. After the flue gas leaves the upper flue gas jacket, it enters the air preheater to preheat the combustion air used by the burner group to realize waste heat recovery. The indirect thermal desorption equipment consumes 20 to 30 m3 of fuel gas to treat contaminated soil. 3 / t.

[0061] (3) Tail gas treatment equipment

[0062] The combustion exhaust in the thermal desorption system is carbon dioxide and water vapor produced after the fuel is fully burned. The fuel gas and combustion-supporting air do not come into contact with the soil and do not involve pollutants in the polluted soil. They can be discharged into the atmosphere after heat exchange and cooling.

[0063] The water vapor, mercury gas, and organic matter gas evaporated from the contaminated soil are drawn into the tail gas treatment equipment. The specific treatment process is as follows:

[0064] 1) Dust removal unit

[0065] Thermal desorption exhaust contains high concentrations of particulate matter. Removing the particles and then condensing the mercury for mercury extraction effectively reduces mercury soot production, thereby improving the quality of the condensed mercury. The dust removal unit utilizes a cyclone dust collector and a bag filter for dust removal. The cyclone uses the centrifugal force generated by a rotating airflow to separate dust particles from the mixed airflow. The cyclone captures particles larger than 5 to 15 microns, while the bag filter removes smaller particles that the cyclone cannot handle.

[0066] 2) Condensing unit

[0067] The thermal desorption tail gas after the dust removal unit is subjected to a sudden temperature drop by the condensation unit, so that the water vapor, mercury gas and organic gas in the tail gas are condensed into liquid, removing more than 90% of the mercury in the tail gas, and the condensate is input into the wastewater treatment equipment for treatment.

[0068] 3) Gas-liquid separator I

[0069] The water content in the tail gas after condensation is relatively high, and a gas-liquid separator 1 is used to remove the water vapor in the tail gas, and the waste liquid separated by the gas-liquid separator 1 enters the wastewater treatment equipment for treatment.

[0070] 4) Adsorption unit I

[0071] A two-stage activated carbon adsorption process is adopted, that is, two-stage sulfur-loaded and mercury-removing activated carbon boxes are connected in series. The tail gas is adsorbed by the sulfur-loaded and mercury-removing activated carbon to remove pollutants. The sulfur-loaded and mercury-removing activated carbon used is based on activated carbon, and elemental sulfur with a strong affinity for mercury is added. It has a developed internal pore structure, a large specific surface area, a strong adsorption capacity, and a high adsorption efficiency for mercury.

[0072] 5) Washing unit

[0073] Mercury concentrations in contaminated soil exceed standards. To ensure that mercury emissions in tail gas meet standards, a scrubbing unit is installed. When tail gas enters the scrubbing unit, an oxidation reaction occurs under acidic conditions, converting mercury into a dissolved state and converting it from gas to liquid, an irreversible reaction. Organic pollutants are further oxidized and decomposed into CO2 and H2O, achieving purification. The scrubbing liquid produced in the scrubbing unit is then processed in a wastewater treatment facility.

[0074] 6) Gas-liquid separator II

[0075] The water content in the tail gas after the above treatment is relatively high, so a gas-liquid separator II is used to remove the water vapor in the tail gas, and the wastewater separated by the gas-liquid separator II enters the wastewater treatment equipment for treatment.

[0076] 7) Adsorption unit II

[0077] Adsorption unit II is the last step in tail gas treatment. It adopts a two-stage sulfur-loaded mercury-removing activated carbon adsorption process, that is, two-stage sulfur-loaded mercury-removing activated carbon boxes are connected in series. The tail gas enters the terminal sulfur-loaded mercury-removing activated carbon for adsorption to further remove residual mercury, petroleum hydrocarbons, smoke dust, etc. in the tail gas.

[0078] (4) Wastewater treatment equipment

[0079] The condensate, washing wastewater and gas-liquid separation wastewater generated during the thermal desorption treatment process are collected in a collection pool. The collected wastewater enters the integrated water treatment equipment and is treated using a combined process of "chemical oxidation + neutralization flocculation precipitation + activated carbon adsorption". After the treatment meets the standards, it is discharged into the pipe.

[0080] The specific process is as follows:

[0081] The collected wastewater enters the wastewater treatment equipment for treatment. The wastewater treatment equipment is equipped with a regulating tank, an oxidation tank and a flocculation sedimentation tank. The collected wastewater is transported to the regulating tank to adjust the water quality and quantity. Then, the pH value of the wastewater is adjusted in the oxidation tank. An oxidant (Fenton oxidation) is added to react with the pollutants to cause the mercury pollutants in the wastewater to exist in the form of ions. The petroleum hydrocarbons (C 10 -C 40 ) is oxidized and decomposed into CO2 and H2O. The supernatant from the oxidation pond is discharged into the neutralization flocculation sedimentation tank, where flocculants (alkali, sodium sulfide, PFS+PAC, PAM, etc.) are added to form mercury sulfide precipitates and hydroxide flocs, which precipitate the pollutants. The supernatant from the flocculation sedimentation tank is filtered through an activated carbon tank to absorb pollutants in the wastewater. After filtration, it enters the acceptance support water pool for testing. If the test meets the standards, it will be discharged into the pipeline.

[0082] The contaminated soil is treated by preheating and heating in an indirect thermal desorption double-layer furnace. The petroleum hydrocarbons (C 10 -C 40 ) and mercury were 178.2 mg / kg and 4.6 mg / kg, respectively, with removal rates of 93.2% and 95.1%, both meeting the remediation target value requirements.

[0083] The present invention is aimed at high concentrations of mercury and petroleum hydrocarbons (C 10 -C 40) The thermal desorption remediation system and the corresponding tail gas and wastewater treatment process designed for the remediation of composite contaminated soil solve the problem of high concentrations of mercury and petroleum hydrocarbons (C 10 -C 40 ) It can solve the problems of complex contaminated soil remediation and exhaust gas treatment, such as high equipment energy consumption, and has important engineering application value.

[0084] Any matters not described in the present invention are applicable to the prior art.

[0085] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons, comprising a pretreatment device, an indirect thermal desorption device, an exhaust gas treatment device, and a wastewater treatment device, characterized in that: The indirect thermal desorption equipment includes an upper furnace, a lower furnace and an air preheater. The lower furnace and the upper furnace are both screw-propelled. A natural gas burner and a plurality of burners are arranged below the lower furnace. The lower furnace is provided with a thermal desorption chamber and a lower flue gas jacket. The lower flue gas jacket is arranged around the thermal desorption chamber. The upper furnace is provided with a drying chamber and an upper flue gas jacket. The upper flue gas jacket is arranged around the drying chamber. The lower flue gas jacket is connected to the upper flue gas jacket. The high-temperature flue gas in the upper flue gas jacket enters the air preheater to preheat the air, and the preheated air is transported to the natural gas burner. The contaminated soil to be treated passes through the drying chamber and the thermal desorption chamber in sequence. The high-temperature flue gas generated by the combustion of the natural gas burner enters the lower flue gas jacket and the upper flue gas jacket in sequence, and heats the contaminated soil in the thermal desorption chamber and the drying chamber at high temperature. The water vapor, mercury gas and organic gas evaporated from the drying chamber and the thermal desorption chamber are transported to the exhaust gas treatment equipment for treatment. The waste liquid generated in the process of treating the exhaust gas by the exhaust gas treatment equipment enters the wastewater treatment equipment for treatment.

2. The thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to claim 1, characterized in that: The natural gas burner generates high-temperature flue gas of 800-1200° C., and the contaminated soil is heated to 450-550° C. in the thermal desorption chamber for a residence time of 15-20 minutes.

3. The thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to claim 2, characterized in that: The tail gas treatment equipment includes: The dust removal unit separates the dust particles in the thermal desorption exhaust gas from the dust-containing airflow; A condensation unit, wherein the temperature of the thermal desorption tail gas after being treated by the dust removal unit is suddenly reduced by the condensation unit, water vapor, mercury gas and organic matter gas in the thermal desorption tail gas are condensed, and the condensate is input into the wastewater treatment equipment for treatment; The gas-liquid separator I performs gas-liquid separation on the condensed tail gas and inputs the separated waste liquid into the wastewater treatment equipment for treatment; Adsorption unit I, using a two-stage activated carbon adsorption process, removes pollutants by subjecting the tail gas separated by the gas-liquid separator I to adsorption treatment on sulfur-loaded and mercury-removing activated carbon; The washing unit collects the tail gas discharged from the adsorption unit I and performs an oxidation reaction under acidic conditions to convert the mercury-containing substances in the tail gas from gaseous state to dissolved state, and the petroleum hydrocarbons (C 10 -C 40 ) is oxidized and degraded, and the generated waste liquid is input into the wastewater treatment equipment; Gas-liquid separator II, which performs gas-liquid separation on the tail gas treated by the washing unit, and the resulting waste liquid is input into the wastewater treatment equipment; Adsorption unit II, the tail gas separated by the gas-liquid separator II is subjected to sulfur-loaded mercury-removing activated carbon adsorption treatment to eliminate the residual mercury and petroleum hydrocarbons (C 10 -C 40 ) and smoke.

4. The thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to claim 2, characterized in that: The wastewater treatment equipment includes: A regulating tank for collecting waste liquid generated by the tail gas treatment equipment and regulating water quality and quantity; Oxidation tank, adjust the pH value of the wastewater, add oxidant to carry out oxidation reaction so that the mercury pollutants in the wastewater exist in ionic form, and convert the contained petroleum hydrocarbons (C 10 -C 40 ) oxidative decomposition into CO2 and H2O; A neutralization flocculation sedimentation tank is used to collect the supernatant of the oxidation tank and use a flocculant to form mercury sulfide precipitation and hydroxide flocs to precipitate the pollutants; The activated carbon filter collects the supernatant of the neutralization flocculation sedimentation tank, and adsorbs pollutants in the supernatant through the activated carbon filter, and the wastewater after adsorption and filtration meets the discharge standards.

5. The thermal desorption system for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to any one of claims 1 to 4, characterized in that: The pretreatment equipment includes: crushing and screening equipment, moisture content adjustment equipment and conveying equipment. The crushing and screening equipment crushes the excavated contaminated soil, cleans the large particles of slag with a diameter exceeding 30 mm with high-pressure water flow, and transports the soil particles with a diameter less than 30 mm to the indirect thermal desorption equipment through the conveying equipment.

6. A thermal desorption method for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons, using the thermal desorption system according to claims 1-5, characterized in that: The method comprises the following steps: Step 1: crush and screen the excavated contaminated soil, and input the soil with a set particle size into the indirect thermal desorption equipment; Step 2: The contaminated soil enters the drying chamber of the upper kiln for preheating and then enters the thermal desorption chamber of the lower kiln for high-temperature heating. Water vapor, mercury gas, and organic matter gas are generated in the drying chamber and the thermal desorption chamber. Step 3: The tail gas treatment equipment collects water vapor, mercury gas, and organic matter gas generated by the contaminated soil, and passes them through the dust removal unit + condensation unit + gas-liquid separator I + adsorption unit I + washing unit + gas-liquid separator II + adsorption unit II in sequence to remove residual pollutants in the tail gas; Step 4: The wastewater treatment equipment collects the waste liquid generated during the treatment process of the tail gas treatment equipment, and uses chemical oxidation + neutralization flocculation precipitation + activated carbon adsorption to treat it to meet the standards, and then discharges it through the pipe.

7. The thermal desorption method for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to claim 6, characterized in that: In step 3, the condensation unit condenses the dust-removed gas by a sudden temperature drop method, and the condensed tail gas enters the gas-liquid separator I; the gas obtained after treatment in the gas-liquid separator I enters the adsorption unit I, and is filtered and purified by a two-stage series sulfur-loaded and mercury-removing activated carbon adsorption; the purified tail gas enters the scrubbing unit, and an oxidation reaction occurs under acidic conditions, so that the remaining mercury-containing substances in the tail gas are converted from gas to dissolved state, and the petroleum hydrocarbons (C 10 -C 40 ) is oxidized and degraded; the gas treated by the washing unit is then passed through the gas-liquid separator II to remove water vapor, and the remaining tail gas is then adsorbed by the sulfur-loaded mercury-removing activated carbon in the adsorption unit II to remove residual pollutants.

8. The thermal desorption method for treating soil contaminated with high concentrations of mercury and petroleum hydrocarbons according to claim 7, characterized in that: In step 3, a cyclone dust collector and a bag dust collector are sequentially used in the dust removal unit to remove dust from the thermal desorption tail gas.

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