System and method for pretreating sludge through microwave-chemical synergistic dehydration coupling pyrolysis

Abstract

The invention discloses a system and method for pretreating sludge through microwave-chemical synergistic dehydration coupling pyrolysis, and belongs to the technical field of sewage sludge treatment.The method comprises the steps that municipal sludge and a FeCl3 / quick lime composite conditioner are mechanically mixed and then subjected to a microwave reaction, and microwave field distribution is regulated and controlled in real time; and carrying out filter pressing, tail gas treatment and microwave catalytic oxidation to complete microwave-chemical synergistic dehydration coupling pyrolysis pretreatment on the sludge. By constructing a synergistic mechanism of a microwave electromagnetic field and a composite chemical conditioner, directional destruction of a colloid structure and space-time coupling of a pyrolytic reaction are realized on a molecular level. The FeCl3 / quick lime composite conditioner generates an ion polarization effect in a microwave field, quick lime hydration heat release and microwave dielectric heating form a temperature gradient field, conditioner particles are promoted to penetrate through the interior of sludge floc, the combined water conversion efficiency is improved, the microwave heat effect initiates selective cracking of VOCs, and by regulating and controlling the temperature, the VOCs can be effectively decomposed. Bond breaking of long-chain organic matters is promoted to be converted into small molecular substances, and formation of a dioxin precursor is inhibited from the source.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage sludge treatment, and particularly relates to a system and method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge. Background Technique

[0002] With the accelerated progress of urbanization and the continuous expansion of the scale of sewage treatment, the output of sludge shows a sharp increase. Sludge contains a large amount of harmful substances such as organic matter, heavy metals, and pathogens. If not properly treated and disposed of, it will cause serious pollution to the soil, water body, and atmospheric environment, and thus threaten human health and ecological safety. Therefore, sludge disposal has become a major challenge that needs to be solved urgently in the field of environmental engineering. Transporting sludge to a thermal power plant for co-combustion with coal for power generation is an effective way to achieve sludge reduction, harmlessness, and resource utilization. In this way, the organic matter in the sludge releases energy during the combustion process, which can be used for power generation. At the same time, the harmful substances in the sludge are decomposed and fixed at high temperatures to achieve harmless treatment. However, to achieve this goal, the sludge needs to be pretreated, that is, the water in it is removed so that the moisture content and other indicators meet the combustion conditions of the thermal power plant. Otherwise, the high-moisture-content sludge will not only increase the transportation cost but also affect the combustion efficiency and stability.

[0003] At present, in the aspect of sludge dehydration pretreatment, traditional thermal drying, mechanical dehydration and other technologies have been applied to a certain extent. The traditional thermal drying technology uses a heat source (such as steam, hot air, etc.) to heat the sludge to evaporate the water, so as to achieve the purpose of dehydration. However, this technology requires a large amount of energy consumption and high energy consumption, and may produce secondary pollutants such as odor gases during the heating process. The mechanical dehydration technology extrudes the water in the sludge through mechanical force (such as pressure filtration, centrifugation, etc.). Although the energy consumption is relatively low, the dehydration efficiency is limited, and it is difficult to reduce the moisture content of the sludge to a lower level. Relevant research shows that the use of FeCl3 alone can reduce the moisture content of the sludge to about 65%. FeCl3 can react chemically with the colloidal substances in the sludge, change the particle structure and surface properties of the sludge, and promote water removal. However, the use of FeCl3 will introduce chloride ions, and there is a risk of chloride ion residue, which may cause adverse effects such as corrosion to the subsequent combustion process and equipment. Although microwave dehydration alone can use the thermal effect of microwaves to destroy the cell structure of the sludge and accelerate water evaporation, the unit treatment energy consumption is as high as 2.5 kWh / kg of water-containing sludge, and the operating cost is relatively high. In addition, the invention purposes of similar technical solutions mainly focus on the improvement of single dehydration efficiency or the optimization of simple chemical conditioning, lacking systematicness and comprehensiveness, and not considering various factors and influences in the sludge dehydration process as a whole.

[0004] The conventional chemical conditioner has the defect of insufficient action depth in destroying the sludge colloidal structure, making it difficult to fundamentally improve the dewatering performance of sludge. The sludge colloidal structure is complex, and conventional chemical conditioners often only act on the surface of sludge particles and cannot penetrate into the particles, resulting in unsatisfactory dewatering effects. More critically, the existing technology lacks effective means to control the release of volatile organic compounds (VOCs) during the dewatering process. During the sludge dewatering process, due to changes in conditions such as temperature and pressure, the organic matter in the sludge will decompose and volatilize, generating a large amount of VOCs. VOCs not only have a pungent smell, pollute the surrounding environment, and affect the quality of life of residents, but also in the subsequent incineration process, some components of these VOCs may participate in the formation reaction of highly toxic substances such as dioxins, increasing the environmental risk during the incineration process. In addition, the sludge filtrate generated during the sludge dewatering process contains high concentrations of pollutants such as organic matter and heavy metals, which will also cause secondary pollution to the water environment if not properly treated. These technical bottlenecks seriously restrict the process of sludge resource utilization, and the existing technology fails to effectively solve the coordination problem between dewatering efficiency and secondary pollution control, making it difficult to meet the actual needs of safe, efficient, and environmentally friendly sludge disposal. Summary of the Invention

[0005] In order to overcome the above-mentioned disadvantages of the existing technology, the purpose of the present invention is to provide a system and method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, so as to solve the technical problems of low sludge dewatering efficiency, insufficient control of secondary pollution, and insufficient action depth of traditional chemical conditioners at the molecular level, and at the same time optimize the dewatering process and tail gas treatment system to form an efficient, environmentally friendly, and economical sludge resource utilization technology system.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising the following steps: After mechanically mixing and stirring municipal sludge with a FeCl3 / calcium oxide composite conditioner, a microwave reaction is carried out, and the microwave field distribution is regulated in real time; after pressure filtration, tail gas treatment, and microwave catalytic oxidation, the microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge is completed.

[0007] Preferably, the addition amount of the FeCl3 / calcium oxide composite conditioner is 3%-5% of the mass of the municipal sludge.

[0008] Preferably, the FeCl3 / calcium oxide composite conditioner includes 0.3% - 0.8% of diatomite.

[0009] Preferably, the molar ratio of FeCl3 to calcium oxide in the FeCl3 / calcium oxide composite conditioner is 1: (1 - 3).

[0010] Preferably, the time for mechanical mixing and stirring is 10 to 20 min.

[0011] Preferably, the frequency of the microwave reaction is 2.45 GHz; the power density is 10 to 20 W / g; the dielectric loss factor is 0.3 - 0.5.

[0012] Preferably, the temperature of the microwave reaction is 300 to 400 °C, and the irradiation time is 8 - 12 min.

[0013] Preferably, the pressure gradient for pressure filtration is 0.8 - 1.2 MPa; the time for pressure filtration is 3 h; the temperature for tail gas treatment is 180 °C.

[0014] Preferably, a molecular sieve-supported Fe-Mn catalyst is used for microwave catalytic oxidation.

[0015] The present invention also discloses a system for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising: a stirrer, a multi-mode resonant cavity microwave reactor, and a tail gas treatment pipeline connected in sequence; Municipal sludge and an FeCl3 / calcium oxide composite conditioning agent are mechanically mixed and stirred in the stirrer, a microwave reaction is carried out in the multi-mode resonant cavity microwave reactor, and tail gas treatment and microwave catalytic oxidation are carried out in the tail gas treatment pipeline.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, constructs a ternary synergistic system of microwave electromagnetic field-chemical conditioning agent-porous medium, and realizes the directional regulation of sludge water forms through the coupling effect of dielectric loss and ionic polarization; proposes a new method for spatio-temporal coupling of dehydration and pyrolysis processes, and uses the selective heating characteristic of microwaves to achieve in-situ degradation of VOCs while dehydrating; proposes a dynamic regulation strategy for microwave field based on dielectric parameter feedback, breaks through the energy efficiency bottleneck of traditional equipment, and saves more than 40% energy compared with existing microwave dehydration devices. By constructing the synergistic action mechanism of microwave electromagnetic field and composite chemical conditioning agent, technical problems such as low sludge dehydration efficiency, insufficient control of secondary pollution, and insufficient action depth of traditional chemical conditioning agents are solved at the molecular level. At the same time, the dehydration process and the tail gas treatment system are optimized to form an efficient, environmentally friendly, and economical sludge resource utilization technology system.

[0017] Furthermore, traditional sludge dehydration technologies (such as thermal drying, mechanical dehydration) have problems of high energy consumption and low dehydration efficiency, and it is difficult to reduce the sludge moisture content to a lower level. The present invention constructs the synergistic action mechanism of microwave electromagnetic field and composite chemical conditioning agent (FeCl3 / calcium oxide), realizes the directional destruction of colloidal structure and the spatio-temporal coupling of pyrolysis reaction at the molecular level, significantly improves the conversion efficiency of bound water, and increases the dehydration efficiency by more than 3 times.

[0018] Furthermore, the existing methods lack effective means to control the release of volatile organic compounds (VOCs) during the dehydration process, resulting in potential risks of dioxin formation in subsequent incineration. The present invention selectively cracks VOC components through microwave thermal effects, regulates the reaction temperature in the range of 300 - 400 °C, promotes the breaking of long-chain organic compounds into small molecules, and inhibits the formation of dioxin precursors from the source.

[0019] Furthermore, conventional chemical conditioners have the defect of insufficient depth of action in destroying the sludge colloidal structure, making it difficult to fundamentally improve the sludge dewatering performance. The FeCl3 / calcium oxide composite formula of the present invention generates an ionic polarization effect in the microwave field. The heat released by the hydration of calcium oxide and the microwave dielectric heating form a temperature gradient field, promoting the penetration of conditioner particles into the interior of sludge flocs and achieving deep conditioning.

[0020] Furthermore, traditional thermal drying technologies consume a large amount of energy and have high operating costs. The present invention uses microwave dielectric heating technology, directly acting on the interior of the sludge by the microwave field, reducing energy loss and improving energy utilization efficiency.

[0021] Furthermore, traditional plate and frame filter presses have a long pressure holding time and low processing efficiency. When the dehydrated sludge of the present invention is processed by a plate and frame filter press, the pressure filtration pressure gradient is controlled in the range of 0.8 - 1.2 MPa, and the pressure holding time is shortened to 1 / 3 of the traditional process, significantly improving the processing efficiency.

[0022] Furthermore, existing tail gas treatment technologies are difficult to efficiently remove VOCs and have a risk of secondary pollution. The tail gas treatment system designed by the present invention integrates a microwave catalytic oxidation unit, uses a molecular sieve-supported Fe-Mn catalyst, and achieves a VOC removal rate > 90% under the working condition of 180 °C, effectively controlling secondary pollution.

[0023] Furthermore, during the existing microwave irradiation process, the internal temperature distribution of the material is uneven, affecting the dewatering effect. The present invention adjusts the microwave field distribution in real time through an online dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material and optimize the dewatering process.

[0024] Furthermore, existing single conditioners are difficult to meet the comprehensive requirements of sludge dewatering and resource utilization. The FeCl3 / calcium oxide composite conditioner of the present invention specifically adds 0.5% diatomite as a microwave sensitizing medium to enhance the microwave absorption and heat conduction performance and improve the conditioning effect.

[0025] Furthermore, existing links such as sludge dewatering and tail gas treatment are independent of each other and lack coordinated optimization. The present invention forms a complete sludge resource utilization technology chain through the integrated design of a multi-mode resonant cavity microwave reactor and a tail gas treatment system, realizing the optimization and coordination of the process flow.

[0026] Furthermore, existing sludge treatment technologies suffer from high energy consumption, high costs, and low efficiency, making them difficult to meet the needs of large-scale applications. This invention, through multidisciplinary innovation, significantly improves sludge dewatering efficiency and resource utilization, while reducing the risk of secondary pollution, forming a highly efficient, environmentally friendly, and economical sludge treatment technology system.

[0027] The present invention also discloses a system for pre-treating sludge by microwave-chemical synergistic dehydration coupled with pyrolysis. The system significantly improves the sludge dehydration efficiency through microwave-chemical synergy, achieves energy saving by combining dynamic regulation of dielectric parameters, and utilizes the selective heating characteristics of microwaves to degrade VOCs in situ during the dehydration process. The integrated tail gas microwave catalytic oxidation module ensures efficient pollution control, ultimately obtaining a sludge with low moisture content and high calorific value, forming a sludge resource treatment system that is efficient, environmentally friendly, and energy-saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of thermogravimetry-differential scanning calorimetry of sludge after treatment using the method for pre-treating sludge by microwave-chemical synergistic dehydration coupled with pyrolysis disclosed in Example 1 of the present invention; Figure 2 This is a high-magnification scanning electron microscope image of sludge after treatment using the method for pre-treating sludge by microwave-chemical synergistic dehydration coupled with pyrolysis disclosed in Example 1 of the present invention; Figure 3 This is a small-magnification scanning electron microscope image of sludge after treatment using the method for pre-treating sludge by microwave-chemical synergistic dehydration coupled with pyrolysis disclosed in Example 1 of the present invention; Figure 4 This is a schematic diagram of the method for pre-treating sludge by microwave-chemical synergistic dehydration coupled with pyrolysis according to the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0031] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0032] In the present invention, unless otherwise specified, percentages (%) or parts refer to percentages by weight or parts by weight relative to the composition.

[0033] In the present invention, unless otherwise specified, the various components involved or their preferred components can be combined with each other to form a new technical solution.

[0034] In the present invention, unless otherwise stated, the numerical range "a~b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been fully listed herein, and "6~22" is only an abbreviated representation of these numerical combinations.

[0035] The "range" disclosed in the present invention can be in the form of one or more lower limits and one or more upper limits respectively.

[0036] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0037] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in order. Preferably, the reaction method herein is carried out sequentially.

[0038] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to persons skilled in the art. In addition, any method or material similar or equivalent to the recorded content can also be applied to the present invention.

[0039] A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge disclosed in the present invention comprises the following steps: Step 1: Mechanically mix and stir municipal sludge with a moisture content of 80% and an FeCl3 / calcium oxide composite conditioner with a mass ratio of 3%-5% (molar ratio 1:(1~3)). 0.3%~0.8% diatomite is specially added as a microwave sensitizing medium in the FeCl3 / calcium oxide composite conditioner. The mechanical mixing and stirring time is 10~20 min. A double-screw stirrer is used with a rotation speed of 60 rpm to ensure uniform dispersion of the agent; Step 2: Place the mixture in step 1 in a multi-mode resonant cavity microwave reactor and irradiate it for 8-12 min under the conditions of a frequency of 2.45 GHz and a power density of 10~20 W / g. In this stage, the microwave field distribution is regulated in real time through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material. Inside the multi-mode resonant cavity microwave reactor, the dosage is adjusted according to the feedback of the on-line system, and the temperature is regulated to maintain the optimal energy coupling state (dielectric loss factor 0.3-0.5).

[0040] Step 3: The dehydrated sludge in Step 2 is treated by a plate and frame filter press. After adding a composite conditioner, part of the water is removed, achieving the purpose of preliminary dehydration, but it is not sufficient. The treated sludge needs to further remove water. The pressure filtration pressure gradient is controlled in the range of 0.8 - 1.2 MPa, and the pressure holding time is shortened to 1 / 3 of the traditional process. The plate and frame filter press is pressed at 0.8 - 1.2 Mpa for 3 hours and then pressed for 1 hour after conditioning. At the same time, the specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, using a molecular sieve-supported Fe-Mn catalyst to achieve a VOCs removal rate > 90% under the working condition of 180°C. Part of the VOCs in the sludge in the microwave reactor is released into the gas and discharged into the tail gas treatment pipeline. The tail gas treatment pipeline is equipped with an Fe-Mn catalyst according to the gas flow direction, and the temperature here is 180°C. The Fe-Mn catalyst is installed horizontally in the pipeline, similar to activated carbon for water purification.

[0041] Step 1 includes: Step 101: Prepare a composite conditioner by mixing FeCl3 and quicklime at a molar ratio of 1: (1 - 3); Step 102: Mix the composite conditioner in Step 101 with diatomaceous earth evenly at a mass ratio of (99.2 - 99.7): (0.3 - 0.8); Step 103: Mechanically stir and mix the mixture in Step 102 with municipal sludge with a moisture content of 80% at a mass ratio of 3% - 5%.

[0042] The present invention constructs a synergistic action mechanism of microwave electromagnetic field and composite chemical conditioner to achieve the space-time coupling of directional destruction of colloidal structure and pyrolysis reaction at the molecular level. Specifically, the FeCl3 / quicklime composite formula generates an ionic polarization effect in the microwave field. The exothermic hydration of quicklime and microwave dielectric heating form a temperature gradient field, promoting the penetration of conditioner particles into the interior of sludge flocs. This synergistic effect increases the conversion efficiency of bound water by more than 3 times. At the same time, the microwave thermal effect triggers the selective cracking of VOCs components. By controlling the reaction temperature in the range of 300 - 400°C, long-chain organic compounds are broken into small molecules, inhibiting the formation of dioxin precursors from the source.

[0043] The present invention also discloses a system for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising: a stirrer, a multi-mode resonant cavity microwave reactor, and an exhaust gas treatment pipeline connected in sequence; municipal sludge and an FeCl3 / calcium oxide composite conditioner are mechanically mixed and stirred in the stirrer, a microwave reaction is carried out in the multi-mode resonant cavity microwave reactor, and exhaust gas treatment and microwave catalytic oxidation are carried out in the exhaust gas treatment pipeline. By constructing a ternary system of microwave electromagnetic field-chemical conditioner-porous medium, the coupling effect of dielectric loss and ionic polarization is realized. The coagulation effect of FeCl3 destroys the colloidal structure of sludge, calcium oxide adjusts the pH and releases heat, and the porous medium optimizes the heat conduction path. The synergistic effect of the three can directionally regulate the migration paths of bound water and interstitial water in sludge, reduce the sludge specific resistance, and effectively improve the dehydration efficiency compared with the traditional process. Based on the dynamic regulation strategy of real-time feedback of dielectric parameters, through the field strength distribution optimization algorithm of the multi-mode resonant cavity, the microwave energy is targeted to act on the water polarization region, avoiding the energy redundancy of traditional constant power output. The microwave selective heating characteristic realizes the spatio-temporal coupling of dehydration and pyrolysis: dehydration and the cracking of volatile organic compounds are completed synchronously, and the concentration of benzene series compounds in the exhaust gas is reduced. The catalytic oxidation effect of Fe 3+ and microwave radiation produce a synergistic effect, effectively improving the ring-opening and cleavage efficiency of dioxin precursors and reducing the risk of secondary pollution from the source. Through the deep coupling of physical field-chemical field-thermal field, systematic breakthroughs are formed in terms of efficiency improvement, cost control, environmental friendliness, etc., providing an effective solution for sludge disposal.

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] Example 1 A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising the following steps: Step 1: Mechanically mix and stir municipal sludge with a moisture content of 82.3% and an FeCl3 / calcium oxide composite conditioner with a mass ratio of 3% (molar ratio 1:2) for 15 min. 0.5% diatomite is specially added to the conditioner as a microwave sensitizing medium; Step 2: Place the mixture in Step 1 in a multimode resonant cavity microwave reactor, and irradiate it for 10 min under the conditions of a frequency of 2.45 GHz, a power density of 15 W / g, and a dielectric loss factor of 0.4. During this stage, the microwave field distribution is regulated in real time through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material. Step 3: Treat the sludge in Step 2 with a plate and frame filter press, control the pressure gradient of filtration at 1.1 MPa, and shorten the pressure holding time to 1 / 3 of the traditional process. At the same time, a specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, uses a molecular sieve-supported Fe-Mn (molar ratio of 1:2) catalyst, and realizes the removal of VOCs under the working condition of 180°C.

[0046] The operation data of a pilot-scale system with a treatment scale of 100 kg / h shows that after the sludge with an initial moisture content of 82.3% is treated by this technology, the final moisture content is stably in the range of 34.7% - 36.2%, and the dehydration efficiency is increased by 58% compared with the conventional technology.

[0047] Figure 1 It is a thermogravimetric-differential scanning calorimetry schematic diagram of the sludge after being treated by the method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge disclosed in Example 1 of the present invention; it can be seen from the figure that the combined analysis of thermogravimetry-differential scanning calorimetry (TG-DSC) shows that the bound water content is reduced from 21.3% of the original sample to 5.8%.

[0048] The gas chromatography-mass spectrometry detection of the sludge after being treated by the method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge disclosed in Example 1 of the present invention finds that the total amount of VOCs is reduced by 85.6%, the removal rate of benzene series reaches 92.4%, and the content of chlorinated organic compounds is reduced by two orders of magnitude.

[0049] The incineration test confirms that the dioxin toxicity equivalent is reduced from 1.8 ng TEQ / kg of the traditional process to 0.15 ng TEQ / kg, meeting the latest EU emission standards. The full-process energy consumption accounting shows that the unit treatment cost is reduced by 62% compared with the thermal drying technology, showing significant economic and environmental benefits.

[0050] Figure 2 It is a large-magnification scanning electron micrograph of the sludge after being treated by the method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge disclosed in Example 1 of the present invention; Figure 3 It is a small-magnification scanning electron micrograph of the sludge after being treated by the method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge disclosed in Example 1 of the present invention; it can be seen from the figure that the scanning electron microscope (SEM) image shows that the treated sludge presents a honeycomb-like pore structure, and the specific surface area is increased by 8.7 times, which creates a favorable channel for water removal.

[0051] After the sludge is treated by the method for microwave-chemical synergistic dehydration-coupled pyrolysis pretreatment of sludge disclosed in Embodiment 1 of the present invention, the characteristic peak at 1700 cm -1 disappears in the Fourier transform infrared spectrum, confirming that the microwave pyrolysis effectively destroys the functional groups of carboxylic acid VOCs.

[0052] Figure 4 FIG. is a schematic diagram of the method for microwave-chemical synergistic dehydration-coupled pyrolysis pretreatment of sludge of the present invention; it can be seen from the figure that the method for microwave-chemical synergistic dehydration-coupled pyrolysis pretreatment of sludge includes: first, mechanically mixing and stirring municipal sludge with an FeCl3 / calcium oxide composite conditioner in a stirrer, and then performing a microwave reaction in a multi-mode resonant cavity microwave reactor to remove VOCs. After pressure filtration, an Fe-Mn catalyst is placed horizontally in the tail gas treatment pipeline, and tail gas treatment and microwave catalytic oxidation are carried out in the tail gas treatment pipeline.

[0053] Embodiment 2 A method for microwave-chemical synergistic dehydration-coupled pyrolysis pretreatment of sludge, comprising the following steps: Step 1: Mechanically mix and stir municipal sludge with a moisture content of 80% and an FeCl3 / calcium oxide composite conditioner with a mass ratio of 3% (molar ratio 1:2) for 10 min, and 0.5% diatomaceous earth is specially added to the conditioner as a microwave sensitizing medium; Step 2: Place the mixture in Step 1 in a multi-mode resonant cavity microwave reactor, and irradiate it for 10 min under the conditions of a frequency of 2.45 GHz, a power density of 15 W / g, and a dielectric loss factor of 0.3. In this stage, the microwave field distribution is real-time regulated through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material; Step 3: Treat the sludge in Step 2 with a plate and frame filter press, control the pressure filtration pressure gradient at 1.0 MPa, and shorten the pressure holding time to 1 / 3 of the traditional process. At the same time, a specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, uses a molecular sieve-supported Fe-Mn catalyst (molar ratio 1:1), and realizes a VOCs removal rate of 91.2% under the working condition of 180 °C.

[0054] Embodiment 3 A method for microwave-chemical synergistic dehydration-coupled pyrolysis pretreatment of sludge, comprising the following steps: Step 1: Mechanically mix and stir municipal sludge with a moisture content of 80% and an FeCl3 / calcium oxide composite conditioner with a mass ratio of 4% (molar ratio 1:2) for 12 min, and 0.4% diatomaceous earth is specially added to the conditioner as a microwave sensitizing medium; Step 2: Place the mixture in Step 1 in a multi-mode resonant cavity microwave reactor, and irradiate it for 8 min under the conditions of a frequency of 2.45 GHz, a power density of 15 W / g, and a dielectric loss factor of 0.5. During this stage, the microwave field distribution is regulated in real time through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material. Step 3: Treat the sludge in Step 2 with a plate and frame filter press, control the pressure filtration pressure gradient at 1.2 MPa, and shorten the pressure holding time to 1 / 3 of the traditional process. At the same time, a specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, uses a molecular sieve supported Fe-Mn catalyst (molar ratio 1:2), and achieves a VOCs removal rate of 91% under the condition of 180 °C.

[0055] Example 4 A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising the following steps: Step 1: Mechanically mix and stir the municipal sludge with a moisture content of 80% and a FeCl3 / calcium oxide composite conditioner with a mass ratio of 3.5% (molar ratio 1:1) for 20 min. 0.3% diatomite is specially added to the conditioner as a microwave sensitizing medium. Step 2: Place the mixture in Step 1 in a multi-mode resonant cavity microwave reactor, and irradiate it for 9 min under the conditions of a frequency of 2.45 GHz, a power density of 20 W / g, and a dielectric loss factor of 0.4. During this stage, the microwave field distribution is regulated in real time through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material. Step 3: Treat the sludge in Step 2 with a plate and frame filter press, control the pressure filtration pressure gradient at 0.8 MPa, and shorten the pressure holding time to 1 / 3 of the traditional process. At the same time, a specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, uses a molecular sieve supported Fe-Mn catalyst (molar ratio 1:2), and achieves a VOCs removal rate of 97% under the condition of 180 °C.

[0056] Example 5 A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, comprising the following steps: Step 1: Mechanically mix and stir the municipal sludge with a moisture content of 80% and a FeCl3 / calcium oxide composite conditioner with a mass ratio of 5% (molar ratio 1:3) for 16 min. 0.8% diatomite is specially added to the conditioner as a microwave sensitizing medium. Step 2: Place the mixture in Step 1 in a multi-mode resonant cavity microwave reactor, and irradiate it for 12 min under the conditions of a frequency of 2.45 GHz, a power density of 10 W / g, and a dielectric loss factor of 0.3. During this stage, the microwave field distribution is regulated in real time through an on-line dielectric parameter monitoring system to ensure the formation of a stable temperature gradient field inside the material. Step 3: Treat the sludge in Step 2 with a plate and frame filter press, control the pressure filtration gradient at 1.2 MPa, shorten the pressure holding time to 1 / 3 of the traditional process. At the same time, the specially designed tail gas treatment system integrates a microwave catalytic oxidation unit, uses a molecular sieve-supported Fe-Mn catalyst (molar ratio 1:1), and achieves a VOCs removal rate of 94% under the condition of 180 °C.

[0057] Comparative example A method for directly co-firing dried sludge using the waste heat of steam extraction from a steam turbine includes the following steps: Step 1: The wet sludge (with a water content of 80%) is first dehydrated to 60% by a plate and frame filter press. The treated wet sludge is sent to the steam indirect drying system built by the power plant, and the water content of the sludge is reduced to less than 30% using the waste heat of steam extraction from the steam turbine.

[0058] Step 2: The dried sludge is crushed and then mixed with coal in a mass ratio of 5% - 8% through a closed conveying system, and sent to a 660 °C circulating fluidized bed boiler for combustion.

[0059] Step 3: The project is equipped with a flue gas purification system, and an activated carbon injection device is added on the basis of the original electrostatic precipitator, desulfurization and denitrification facilities. Pollutants in the flue gas are adsorbed by injecting activated carbon powder.

[0060] Table 1 Comparison of sludge treatment results disclosed in Examples 4 and 5 of the present invention and the comparative example

[0061] Table 1 shows the comparison of sludge treatment results disclosed in Examples 4 and 5 of the present invention and the comparative examples; it can be seen from Table 1 that compared with the comparative example without a catalyst, Example 4 (Fe-Mn 1:2) and Example 5 (Fe-Mn 1:1) show significant advantages in pollutant removal efficiency. Benzene removal rate: Example 4 (98%) and Example 5 (95%) are respectively 56% and 53% higher than that of the comparative example (42%); formaldehyde removal rate: Example 4 (96%) and Example 5 (93%) are respectively 58% and 55% higher than that of the comparative example (38%); total VOCs removal rate: Example 4 (97%) and Example 5 (94%) are respectively 57% and 54% higher than that of the comparative example (40%). The Fe-Mn agent significantly improves the degradation efficiency of pollutants through redox reactions, especially for highly toxic substances such as benzene and formaldehyde, and the removal rate jumps from less than 50% to over 90%. The catalytic activity of the Fe-Mn ratio of 1:2 (Example 4) is better than that of 1:1 (Example 5), indicating that an increase in Mn content may enhance the activity of oxygen vacancies and promote the generation of free radicals (such as ·OH), thereby more efficiently decomposing organic substances. Adding a catalyst pretreatment before sludge co-incineration can significantly reduce the generation of secondary pollutants such as VOCs and benzene series during the combustion process, reduce the load of end-of-pipe flue gas purification, and ensure that the emissions meet strict standards.

[0062] In summary, for the system and method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge of the present invention, by microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, the conversion efficiency of bound water is significantly improved (more than 3 times), the pressure-holding time of plate-and-frame filtration is shortened to 1 / 3 of the traditional process. At the same time, the selective cracking of VOCs is realized by the microwave thermal effect (the long-chain organic compounds are broken in the range of 300-400 °C) and the precursor of dioxin is suppressed at the source. And the tail gas treatment system integrating the microwave catalytic oxidation unit realizes the VOCs removal rate > 90% at 180 °C, forming an efficient, environmentally friendly and economical sludge resource utilization technology system. The sludge dehydration efficiency is greatly improved. After the sludge with an initial moisture content of 82.3% is treated by this technology, the final moisture content is reduced to 34.7-36.2%, and the dehydration efficiency is increased by 58% compared with the conventional technology. The bound water content is reduced from 21.3% of the original sample to 5.8%; the generation of dioxin precursors is effectively suppressed. The incineration test proves that the dioxin toxicity equivalent is reduced from 1.8 ng TEQ / kg of the traditional process to 0.15 ng TEQ / kg, meeting the latest EU emission standards; the pollutant emissions are significantly reduced, the total amount of VOCs is reduced by 85.6%, the removal rate of benzene series reaches 92.4%, and the content of chlorinated organic compounds is reduced by two orders of magnitude; the treated sludge shows a honeycomb-like pore structure, and the specific surface area is increased by 8.7 times, which creates a favorable channel for water removal; the microwave pyrolysis effectively destroys the functional groups of carboxylic acid VOCs and suppresses the generation of toxic and harmful substances at the source; the whole-process energy consumption accounting shows that the unit treatment cost is reduced by 62% compared with the thermal drying technology, with significant economic and environmental benefits.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, characterized in that, It includes the following steps: After mechanically mixing and stirring municipal sludge with FeCl3 / calcium oxide composite conditioner, carry out microwave reaction and regulate the microwave field distribution in real time; After pressure filtration, tail gas treatment and microwave catalytic oxidation, complete the microwave-chemical synergistic dehydration and coupled pyrolysis pretreatment of sludge.

2. The method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge according to claim 1, characterized in that, The addition amount of the FeCl3 / calcium oxide composite conditioner is 3%-5% of the mass of municipal sludge.

3. The method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge according to claim 1, wherein The FeCl3 / calcium oxide composite conditioner contains 0.3% - 0.8% of diatomite.

4. The method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge according to claim 1, characterized in that, In the FeCl3 / calcium oxide composite conditioner, the molar ratio of FeCl3 to calcium oxide is 1:(1 - 3).

5. The method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge according to claim 1, wherein The time of the mechanical mixing and stirring is 10 - 20 min.

6. The method for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge according to claim 1, wherein The frequency of the microwave reaction is 2.45 GHz; the power density is 10 - 20 W / g; the dielectric loss factor is 0.3 - 0.

5.

7. The method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge according to claim 1, wherein, The temperature of the microwave reaction is 300 - 400 °C, and the irradiation time is 8 - 12 min.

8. The method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge according to claim 1, wherein The pressure gradient of the pressure filtration is 0.8 - 1.2 MPa; the time of the pressure filtration is 3 h; the temperature of the tail gas treatment is 180 °C.

9. The method for microwave-chemical synergistic dehydration coupling pyrolysis pretreatment of sludge according to claim 1, characterized in that Use a molecular sieve supported Fe-Mn catalyst for microwave catalytic oxidation.

10. A system for microwave-chemical synergistic dehydration coupled with pyrolysis pretreatment of sludge, characterized in that, It includes: A stirrer, a multi-mode resonant cavity microwave reactor and a tail gas treatment pipeline connected in sequence; The municipal sludge and the FeCl3 / calcium oxide composite conditioner are mechanically mixed and stirred in the stirrer, the microwave reaction is carried out in the multi-mode resonant cavity microwave reactor, and the tail gas treatment and microwave catalytic oxidation are carried out in the tail gas treatment pipeline.

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