A household garbage leachate pyrolysis gas upgrading system and method

Abstract

This invention discloses a system and method for upgrading fuel gas from municipal solid waste leachate pyrolysis, belonging to the field of municipal solid waste treatment and resource utilization technology. The system consists of a lanthanum-iron co-modified sludge biochar catalyst preparation unit, a leachate heterogeneous Fenton pre-modification unit, a catalytic atomization and re-spraying unit, a cascade pyrolysis and gasification unit, a fuel gas deep purification unit, and an intelligent self-response control unit. Using highly active lanthanum-iron co-modified porous sludge biochar as a catalyst, the system first decomposes recalcitrant macromolecules in the leachate into smaller organic molecules through a continuous flow heterogeneous Fenton reaction. Then, the pre-modified leachate is mixed with the catalyst and atomized and re-sprayed into the pyrolysis zone of the pyrolysis furnace, where it undergoes cascade pyrolysis and gasification simultaneously with the municipal solid waste. This achieves the harmless treatment and resource utilization of the leachate, significantly improves the calorific value of the pyrolysis fuel gas, reduces the tar content in the fuel gas, and allows the pyrolysis slag to be directly used in the preparation of building materials, increasing pyrolysis efficiency by more than 20%.

Description

Technical Field

[0001] This invention relates to the field of municipal solid waste pyrolysis gasification and leachate deep treatment technology, and is particularly applicable to the co-treatment of leachate from low-calorific-value municipal solid waste pyrolysis systems in cold and arid urban areas and the preparation of high-value fuel gas. Specifically, it relates to a system and method for upgrading fuel gas based on municipal solid waste leachate pyrolysis. Background Technology

[0002] With the acceleration of urbanization and the improvement of residents' living standards in my country, the amount of urban domestic waste generated has been increasing year by year. In 2021, the amount of urban domestic waste collected in my country reached 248 million tons. Sanitary landfill and pyrolysis gasification are currently the main methods of domestic waste treatment in my country. Among them, pyrolysis gasification technology has been widely used due to its advantages such as high volume reduction, good resource recovery effect, and low secondary pollution.

[0003] However, there are still many problems in the pyrolysis and gasification process of municipal solid waste: First, the calorific value of the pyrolysis gas is low, usually only 8-12 MJ / m³. 3 First, it is difficult to use it directly as industrial or domestic fuel; second, a large amount of tar is generated during the pyrolysis process, which not only reduces the quality of the gas, but also easily clogs pipelines and equipment, increasing operation and maintenance costs; third, the pyrolysis process is greatly affected by the composition and calorific value fluctuations of domestic waste, resulting in poor operational stability.

[0004] Meanwhile, municipal solid waste sanitary landfills and pyrolysis gasification plants generate large amounts of high-concentration leachate. Leachate has a complex composition, containing a large amount of recalcitrant macromolecular humic substances, ammonia nitrogen, heavy metals, and other pollutants, making treatment difficult and costly. Traditional leachate treatment processes suffer from problems such as long process flows, high operating costs, and the generation of large amounts of sludge and concentrate. For example, CN113998840A discloses a method for the full-volume treatment of leachate from municipal solid waste landfills, including the following steps: (1) homogenization; (2) pretreatment; (3) solid-liquid separation; (4) nitrification and denitrification treatment; (5) aerobic fermentation; (6) catalytic strong oxidation treatment; and (7) deep biochemical denitrification treatment. Pretreatment involves adding slaked lime, modified bentonite, and flocculants. Through homogenization, pretreatment, and multi-stage reaction treatment technologies, the problem of leachate treatment from municipal solid waste landfills has been solved. CN116239221B discloses a method for treating landfill leachate, comprising the following steps: mixing nitrogen-containing landfill leachate and activated sludge, and then feeding the mixture into a denitrification tank. Under conditions that inhibit nitrous oxide reduction, the nitrite in the mixture is converted into nitrous oxide gas dissolved in the wastewater by denitrifying bacteria in the denitrification tank; the mixture is then fed into an ammonification tank for gas-liquid separation to collect the nitrous oxide gas; and the wastewater is obtained after ammonification treatment by ammonifying bacteria in the ammonification tank; the wastewater is further fed into a nitrification tank, where nitrite-containing wastewater is obtained under the action of nitrifying bacteria; the wastewater is then returned to the denitrification tank for recycling; and finally, the wastewater is introduced into a separator for separation to obtain dischargeable effluent and wastewater requiring recirculation treatment. By inhibiting nitrous oxide reduction and short-cut nitrification, the landfill leachate treatment process is controlled, solving the problems of N2O generation and emission in existing technologies, and reducing costs and environmental pollution.

[0005] Re-injecting leachate into a pyrolysis furnace for incineration is a potential resource recovery approach. However, leachate typically contains over 60% macromolecular humic substances and fulvic acid, leading to incomplete gasification when directly injected into the primary combustion chamber of the pyrolysis furnace. This results in an increase in tar production of over 30%, causing pipe blockage, equipment corrosion, and decreased thermal efficiency. Furthermore, existing gas catalytic upgrading technologies often employ precious metal catalysts such as platinum and palladium, which are costly, prone to poisoning and deactivation, and not integrated with leachate treatment, making it difficult to achieve the circular economy goal of treating waste with waste. The loss on ignition of pyrolysis furnace slag is generally higher than 5%, resulting in low resource utilization value. Moreover, heavy metals in the leachate are easily migrated with the pyrolysis residue, posing a risk of secondary pollution. Furthermore, directly re-injecting the original leachate will cause a sharp drop in the temperature of the pyrolysis furnace, reduce pyrolysis efficiency, and further decrease the calorific value of the fuel gas. At the same time, the incomplete combustion of large molecular organic matter will produce more toxic and harmful substances such as tar and dioxins. For example, CN102211794B discloses a method for treating leachate by burning landfill gas in a foam bed and evaporating it. Landfill gas or biogas and evaporative combustion air are introduced into the burner, and high-temperature fuel gas is generated after combustion. The high-temperature fuel gas evaporates the injected primary leachate in the primary evaporation chamber and forms a medium-temperature evaporation chamber. The medium-temperature mixed gas passes through the vent cap and enters the secondary evaporation chamber, where it undergoes heat and mass transfer with the injected secondary leachate, causing the leachate to evaporate and forming a low-temperature mixed gas. After passing through the dust collector, the low-temperature mixed gas enters the flare burner, where it is incinerated at high temperature along with the flare landfill gas and combustion air. This landfill gas combustion bubble bed technology evaporates and treats the leachate from the landfill, solving the problem of difficult treatment of high-concentration ammonia nitrogen and humic acid, and achieving energy-saving and volume reduction of leachate emissions and greenhouse gas emission reduction.

[0006] Sludge biochar is a carbon-based material prepared from wastewater sludge from municipal wastewater treatment plants. It boasts advantages such as wide availability, low cost, and well-developed porous structure. Metal modification can significantly enhance the catalytic activity of sludge biochar, enabling it to exhibit excellent performance in heterogeneous Fenton reactions. Currently, research has explored the use of modified sludge biochar for the advanced treatment of leachate; however, a technology combining it with municipal solid waste pyrolysis and gasification to achieve catalytic pyrolysis of leachate and upgrading of fuel gas has not yet been reported. Therefore, developing a system and method that can simultaneously address the challenges of leachate treatment and the low quality of fuel gas from municipal solid waste pyrolysis and gasification has significant practical implications and application value. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, the present invention aims to provide a system and method for upgrading the quality of pyrolysis fuel gas from municipal solid waste leachate. This system utilizes lanthanum-iron synergistic catalysis to achieve efficient decomposition of macromolecular organic matter in leachate and deep reforming of pyrolysis tar, enhances the positive heat exchange effect of leachate re-injection, significantly improves the calorific value and quality of pyrolysis fuel gas from municipal solid waste, reduces tar content, ensures stable operation of the pyrolysis process, and achieves the harmless treatment and resource utilization of leachate.

[0008] To achieve the above objectives, this invention proposes a gas upgrading system based on municipal solid waste leachate pyrolysis. This system comprises six parts: a lanthanum-iron co-modified sludge biochar catalyst preparation unit, a leachate heterogeneous Fenton pre-modification unit, a catalytic atomization and re-injection unit, a cascade pyrolysis gasification unit, a gas deep purification unit, and an intelligent self-response control unit. The lanthanum-iron co-modified sludge biochar catalyst preparation unit is used to prepare porous sludge biochar catalyst supported on lanthanum-iron bimetals. It is sequentially connected to a sludge pretreatment device, a KOH activation device, a co-impregnation device, a tubular pyrolysis furnace, and a catalyst storage tank. The KOH activation device is used to prepare a porous sludge biochar support, and the co-impregnation device is used to impregnate the porous biochar support with a mixed aqueous solution of lanthanum chloride and ferric chloride. The leachate heterogeneous Fenton pre-modification unit adopts a continuous flow heterogeneous Fenton reactor and uses the lanthanum-iron co-modified sludge biochar as a catalyst to decompose the large molecular humic substances in the leachate into small molecular easily gasifiable organic matter. The catalytic atomization and re-spraying unit atomizes and re-sprays the mixture of pre-modified filtrate and catalyst back into the pyrolysis zone of the pyrolysis furnace, and is sequentially connected to a mixing tank, a high-pressure plunger pump, and a high-pressure atomizing nozzle; the high-pressure atomizing nozzle is installed in the middle of the pyrolysis zone of the pyrolysis furnace, and the atomized particle size is controlled at 50-100μm; The stepped pyrolysis gasification unit is a vertical fixed-bed pyrolysis furnace, which is divided into a drying zone, a pyrolysis zone and a combustion zone from top to bottom, to realize the stepped pyrolysis gasification of municipal solid waste. The furnace body side wall is equipped with multiple temperature sensors, pressure sensors and gas composition online monitoring instruments, which are electrically connected to the intelligent self-response control unit. The gas deep purification unit sequentially removes dust, tar, acidic gases and fine particulate matter from the crude gas, and is sequentially connected to a cyclone dust collector, an electrostatic precipitator, an alkaline scrubbing tower and a dry filter. The intelligent self-response control unit adjusts the pre-modification parameters of the leachate and the catalytic re-injection parameters in real time according to the temperature of the pyrolysis zone and the calorific value and composition of the fuel gas. It is electrically connected to the control valves of the Fenton reactor dosing pump and the catalytic atomization re-injection unit, respectively.

[0009] Another aspect of the present invention provides a method for upgrading municipal solid waste leachate pyrolysis fuel gas based on the above-mentioned system, comprising the following steps: S1. Preparation of lanthanum-iron co-modified sludge biochar catalyst: It is prepared by using residual sludge from urban sewage treatment plants as raw material, through KOH activation, co-impregnation with lanthanum chloride and ferric chloride, and high-temperature pyrolysis; S2. Leachate heterogeneous Fenton pre-modification: The pretreated leachate is sent into a continuous flow heterogeneous Fenton reactor, and the lanthanum-iron co-modified sludge biochar catalyst and hydrogen peroxide are added to decompose macromolecular humic substances. The effluent after the reaction can be used for subsequent catalytic atomization and re-spraying without pH adjustment. S3, Catalytic atomization back spray and pyrolysis gasification: The pre-modified leachate is mixed evenly with the catalyst and atomized back sprayed into the pyrolysis zone of the pyrolysis furnace, where it is pyrolyzed and gasified simultaneously with the municipal solid waste; S4. Deep purification and intelligent control of gas: After deep purification, the crude gas is used to obtain high-value gas. The intelligent self-response control unit adjusts the operating parameters in real time to stabilize the pyrolysis process.

[0010] Preferably, step S1 specifically involves drying the residual sludge from the urban sewage treatment plant at 105°C for 24 hours, then pulverizing it through a 200-mesh sieve to obtain fine sludge powder. Sludge powder and KOH were mixed at a mass ratio of 1:2, deionized water was added and stirred evenly, and the mixture was dried at 80℃ for 12 hours. The mixture was then activated at 500℃ under a nitrogen atmosphere at a heating rate of 5℃ / min for 1 hour. After natural cooling to room temperature, the mixture was washed with water until neutral and dried to obtain a porous sludge biochar carrier with a specific surface area of ​​300-400 m². 2 / g; Prepare a mixed aqueous solution of lanthanum chloride and ferric chloride, controlling the molar ratio of lanthanum to ferric chloride to be 1:(5-20), and the total metal ion concentration to be 0.05-0.1 mol / L; The porous sludge biochar carrier was mixed with a mixed aqueous solution at a solid-liquid ratio of 1:(8-12), and then shaken and impregnated at 37℃ and 160r / min for 24h. After centrifugation at 4000r / min, it was dried at 80℃ for 12h. The temperature was increased to 700℃ at a rate of 10℃ / min under a nitrogen atmosphere, and then pyrolyzed at a constant temperature for 2 hours. The mixture was then naturally cooled to room temperature to obtain a lanthanum-iron co-modified sludge biochar catalyst.

[0011] Preferably, in step S2, the dosage of the lanthanum-iron co-modified sludge biochar catalyst is 0.8-1.5 g / L, the dosage of hydrogen peroxide is 60-90 mmol / L, the reaction pH is 3.0-3.5, the hydraulic retention time is 1.5-2 h, and the decomposition rate of macromolecular humic substances is ≥90%.

[0012] Preferably, in step S3, the mass ratio of the pre-modified leachate to the catalyst is 100:(1-3), and the amount of back spray is 15%-25% of the amount of municipal solid waste fed in.

[0013] Preferably, in step S4, the specific rules for the intelligent self-response control are as follows: When the temperature in the pyrolysis zone is <650℃, increase the amount of pre-modified leachate re-sprayed by 10%-20%; When the calorific value of the gas is <14MJ / m 3 At the same time, increase the catalyst dosage by 0.3-0.6 g / L and simultaneously increase the hydrogen peroxide dosage by 5%-10%; When the tar content in the gas is >3g / m³3 At the same time, increase the temperature of the pyrolysis zone by 30-50℃, and increase the catalyst back-injection ratio to 100:4. When the lower heating value of municipal solid waste is <3800kJ / kg, increase the amount of leachate re-spraying to 25%-30%, and at the same time increase the amount of catalyst added by 0.2-0.4g / L.

[0014] The pyrolysis slag treated by this invention has a heat loss on ignition of ≤3%, and can be directly used to prepare building materials; the lanthanum-iron co-modified sludge biochar catalyst can be recycled more than 20 times, with an activity retention rate of ≥80%; the entire system operates stably, and the pyrolysis efficiency is improved by more than 20%.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Significant synergistic catalytic effect of lanthanum and iron: The introduction of rare earth lanthanum inhibits the aggregation of iron species, improves their dispersibility on the surface of porous biochar, increases the number of oxygen vacancies, and promotes electron transfer. This not only efficiently decomposes large molecular humic substances in leachate but also catalyzes the cracking and reforming reactions of tar during pyrolysis, significantly improving the calorific value and quality of the pyrolysis fuel gas, and reducing the tar content to 0.5 g / m³. 3 The following solutions address the pipeline blockage problem caused by direct back spraying of leachate; the synergistic modification of lanthanum and iron bimetals significantly improves the catalytic activity and stability of sludge biochar, allowing the catalyst to be recycled more than 20 times with an activity retention rate of ≥80%, thus greatly reducing operating costs. 2. Achieved harmless treatment and resource utilization of leachate: After heterogeneous Fenton pre-modification, the leachate is injected back into the pyrolysis furnace, avoiding the high cost and secondary pollution problems of traditional leachate treatment processes. At the same time, the organic matter in the leachate is used as supplementary fuel for pyrolysis gasification, improving the energy utilization rate of the system. 3. By using an intelligent self-response control unit to monitor the temperature and fuel parameters in the pyrolysis zone in real time, and dynamically adjusting the leachate pre-modification and back-injection parameters, the influence of fluctuations in the composition and calorific value of municipal solid waste on the pyrolysis process is effectively offset, and the pyrolysis efficiency is improved by more than 20%. 4. Waste-to-waste treatment with low cost: The pyrolysis slag has a heat loss rate of ≤3%, and the residue can be recycled and directly used to prepare building materials, realizing the full resource utilization of domestic waste; porous biochar carriers are prepared using residual sludge from urban sewage treatment plants as raw materials, realizing the resource utilization of solid waste, and the catalyst cost is only 1 / 20 of that of precious metal catalysts. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined as herein. The reagents used herein may be commercially available related products, and performance testing standards refer to industry or national standards.

[0018] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0019] Experimental materials and equipment Experimental materials Domestic waste: taken from the domestic waste transfer station in the central urban area of ​​Ordos City, crushed to a particle size of ≤50mm, and naturally air-dried to a moisture content of about 30%, with a lower calorific value of 3650kJ / kg; Leachate: taken from a municipal solid waste landfill in Ordos, with COD of 42,500 mg / L, BOD5 of 11,200 mg / L, macromolecular humic content of 68.5%, and pH of 7.8. Excess sludge: taken from the secondary sedimentation tank of a sewage treatment plant in a town in Ordos. Chemical reagents: KOH, lanthanum chloride (LaCl3·7H2O), ferric chloride (FeCl3·6H2O), 30% hydrogen peroxide, sulfuric acid, sodium hydroxide, etc., all of which are analytical grade.

[0020] Experimental equipment Tubular pyrolysis furnace: SK-G08123K type, Tianjin Zhonghuan Experimental Electric Furnace Co., Ltd.; Continuous flow heterogeneous Fenton reactor: self-made, effective volume 5L; Vertical fixed bed pyrolysis furnace: self-made, with a processing capacity of 10 kg / h, divided into a drying zone (200-300℃), a pyrolysis zone (600-800℃), and a combustion zone (800-900℃) from top to bottom; Gasboard-3100 Online Gas Component Analyzer, Wuhan Sifang Optoelectronic Technology Co., Ltd. Tar content analyzer: Determined according to GB / T12208-2008 "Determination of Tar and Dust Content in Urban Gas"; Loss on ignition tester: Tested in accordance with GB16889-2008 "Standard for Pollution Control of Municipal Solid Waste Landfill".

[0021] Example 1 S1. Preparation of Lanthanum-Iron Co-modified Sludge Biochar Catalyst: Wastewater sludge from urban wastewater treatment plants was dried at 105℃ for 24 hours, then pulverized through a 200-mesh sieve to obtain fine sludge powder. The fine sludge powder was mixed with KOH at a mass ratio of 1:2, and deionized water was added and stirred until homogeneous. The mixture was dried at 80℃ for 12 hours, then heated to 500℃ at a rate of 5℃ / min under a nitrogen atmosphere and activated at this temperature for 1 hour. After natural cooling to room temperature, the mixture was washed with water until neutral and dried to obtain a porous sludge biochar carrier with a specific surface area of ​​352 m². 2 / g; Prepare a mixed aqueous solution of lanthanum chloride and ferric chloride, controlling the lanthanum-ferric molar ratio to be 1:10 and the total metal ion concentration to be 0.08 mol / L; Mix the porous sludge biochar support with the mixed aqueous solution at a solid-liquid ratio of 1:10, shake and impregnate at 37℃ and 160 r / min for 24 h, centrifuge at 4000 r / min and dry at 80℃ for 12 h; Heat to 700℃ at a heating rate of 10℃ / min under a nitrogen atmosphere, pyrolyze at a constant temperature for 2 h, and naturally cool to room temperature to obtain the lanthanum-ferric co-modified sludge biochar catalyst; S2. Heterogeneous Fenton Pre-modification of Leachate: The leachate, after pretreatment by removing large particulate matter through a screen, is fed into a continuous flow heterogeneous Fenton reactor. The pH is adjusted to 3.2 with sulfuric acid, and the lanthanum-iron co-modified sludge biochar catalyst prepared above is added at a dosage of 1.2 g / L. 30% hydrogen peroxide is slowly added at a dosage of 75 mmol / L. The hydraulic retention time is 1.8 h. No pH adjustment is required for the effluent after the reaction.

[0022] S3. Catalytic atomization and pyrolysis gasification: The pre-modified leachate and lanthanum-iron co-modified sludge biochar catalyst are mixed evenly at a mass ratio of 100:2. The mixture is then atomized and atomized back into the middle of the pyrolysis zone of the pyrolysis furnace through a high-pressure plunger pump and a high-pressure atomizing nozzle. The atomized particle size is controlled at 70-80μm, and the back-spray amount is 20% of the amount of municipal solid waste fed into the furnace. The municipal solid waste is continuously fed into the vertical fixed bed pyrolysis furnace at a rate of 10kg / h. It undergoes staged pyrolysis and gasification from top to bottom, passing through the drying zone, pyrolysis zone, and combustion zone. The temperature in the pyrolysis zone is controlled at 700℃.

[0023] S4. Deep purification and intelligent control of gas: The crude gas produced by pyrolysis passes through a cyclone dust collector, an electrostatic precipitator, an alkaline scrubbing tower, and a dry filter in sequence to remove dust, tar, acidic gases, and fine particulate matter, resulting in purified high-value gas. The intelligent self-response control unit monitors the temperature of the pyrolysis zone, the calorific value of the gas, and the tar content in real time, and dynamically adjusts the operating parameters according to preset rules to stabilize the pyrolysis process.

[0024] Example 2 This embodiment is basically the same as Example 1, except that in step S1, the molar ratio of lanthanum chloride to ferric chloride is 1:5, the total metal ion concentration is 0.05 mol / L, and the lanthanum-iron co-modified sludge biochar catalyst is prepared.

[0025] Example 3 This embodiment is basically the same as Example 1, except that in step S1, the molar ratio of lanthanum chloride to ferric chloride is 1:20, the total metal ion concentration is 0.1 mol / L, and the lanthanum-iron co-modified sludge biochar catalyst is prepared.

[0026] Example 4 This embodiment is basically the same as Example 1, except that in step S2, the dosage of lanthanum-iron co-modified sludge biochar catalyst is 0.8 g / L, the dosage of hydrogen peroxide is 60 mmol / L, and the hydraulic retention time is 1.5 h.

[0027] Example 5 This embodiment is basically the same as Example 1, except that in step S2, the dosage of lanthanum-iron co-modified sludge biochar catalyst is 1.5 g / L, the dosage of hydrogen peroxide is 90 mmol / L, and the hydraulic retention time is 2 h.

[0028] Example 6 This embodiment is basically the same as embodiment 1, except that in step S3, the mass ratio of pre-modified leachate to catalyst is 100:1, and the amount of back spray is 15% of the amount of municipal solid waste fed in.

[0029] Example 7 This embodiment is basically the same as embodiment 1, except that in step S3, the mass ratio of pre-modified leachate to catalyst is 100:3, and the amount of back spray is 25% of the amount of municipal solid waste fed in.

[0030] Example 8 This embodiment is basically the same as Embodiment 1, except that the following intelligent self-response control rules are used to adjust the operating parameters in real time: When the temperature in the pyrolysis zone is <650℃, increase the amount of pre-modified leachate re-sprayed by 10%-20%; When the calorific value of the gas is <14MJ / m 3 At the same time, increase the catalyst dosage by 0.3-0.6 g / L and simultaneously increase the hydrogen peroxide dosage by 5%-10%; When the tar content in the gas is >3g / m³ 3 At the same time, increase the temperature of the pyrolysis zone by 30-50℃, and increase the catalyst back-injection ratio to 100:4. When the lower heating value of municipal solid waste is <3800 kJ / kg, the leachate re-injection rate is increased to 25%-30%, and the catalyst dosage is increased by 0.2-0.4 g / L. During the experiment, the lower heating value of municipal solid waste fluctuated between 3200-4100 kJ / kg, the initial temperature of the pyrolysis zone was 620℃, and the initial heating value of the fuel gas was 13.2 MJ / m³. 3 The initial tar content was 3.5 g / m³. 3 .

[0031] Comparative Example 1 This comparative example is basically the same as Example 1, except that: no catalyst is used, and no heterogeneous Fenton pre-modification of leachate is carried out. The original leachate is directly atomized and sprayed back into the pyrolysis zone of the pyrolysis furnace. The amount of back spraying is 20% of the amount of municipal solid waste fed in.

[0032] Comparative Example 2 This comparative example is basically the same as Example 1, except that: unmodified sludge biochar (SBC) is used instead of lanthanum-iron co-modified sludge biochar catalyst for heterogeneous Fenton pre-modification and catalytic atomization re-spraying of leachate.

[0033] Comparative Example 3 This comparative example is basically the same as Example 1, except that: single iron-modified sludge biochar (Fe / SBC) is used instead of lanthanum-iron co-modified sludge biochar catalyst for heterogeneous Fenton pre-modification and catalytic atomization re-spraying of leachate. The preparation method of Fe / SBC is as follows: porous sludge biochar support is mixed with a 0.08 mol / L ferric chloride aqueous solution at a solid-liquid ratio of 1:10, and the remaining steps are the same as in Example 1.

[0034] Comparative Example 4 This comparative example is basically the same as Example 1, except that: the leachate is not subjected to heterogeneous Fenton pre-modification, and the lanthanum-iron co-modified sludge biochar catalyst is directly mixed with the original leachate at a mass ratio of 100:2, and then atomized and sprayed back into the pyrolysis zone of the pyrolysis furnace. The amount of back spraying is 20% of the amount of municipal solid waste fed in.

[0035] Comparative Example 5 This comparative example is essentially the same as Example 8, except that: the intelligent self-response control system is not used; instead, fixed parameters are employed, namely, the leachate re-spraying volume is fixed at 20%, the catalyst dosage is fixed at 1.2 g / L, the hydrogen peroxide dosage is fixed at 75 mmol / L, and the pyrolysis zone temperature is fixed at 700℃. During the experiment, the fluctuation range of the lower heating value of municipal solid waste was the same as in Example 8.

[0036] The test results of the above embodiments and comparative examples are shown in Table 1. As can be seen from Table 1, in Comparative Example 2, the unmodified sludge biochar showed a decomposition rate of only 35.2% for macromolecular humic substances, a COD removal rate of 21.7%, and a B / C ratio that only increased from 0.26 to 0.32, indicating extremely low catalytic activity. In Comparative Example 3, the decomposition rate of the single iron-modified sludge biochar increased to 68.9%, but still could not meet the requirements for industrial applications. The lanthanum-iron co-modified sludge biochar catalyst prepared in this invention, as shown in Examples 1-3, showed a decomposition rate of ≥90% for macromolecular humic substances, with the optimal ratio (La:Fe=1:10) achieving a decomposition rate of 92.7%, a COD removal rate of 67.2%, and a B / C ratio increase to 0.71. It is evident that the introduction of rare earth lanthanum produced a triple synergistic effect: firstly, a steric hindrance effect, as the radius of lanthanum ions is much larger than that of iron ions, effectively inhibiting the aggregation of iron species and significantly improving the dispersion of iron species; secondly, an electron transfer effect, where La... 3+ with Fe 3+ Electron transfer channels are formed between them, accelerating the Fe... 3+ To Fe 2+ The reduction process solves the bottleneck problem of traditional heterogeneous Fenton reactions; thirdly, the oxygen vacancy generation effect, lanthanum doping leads to lattice distortion of biochar, generating a large number of oxygen vacancies, realizing ·OH and ·O 2- Synergistic oxidation by two free radicals.

[0037] Comparing the data from Comparative Example 4 and Example 1 in Table 1, it can be seen that heterogeneous Fenton pre-modification is an indispensable core step of this invention. Comparative Example 4 used the same lanthanum-iron co-modified catalyst, but without heterogeneous Fenton pre-modification, and directly mixed it with the original leachate for re-injection, resulting in a fuel gas calorific value of only 12.8 MJ / m³. 3 The tar content is 1.5g / m³. 3 In Example 1, after heterogeneous Fenton pre-modification, the calorific value of the gas reached 16.5 MJ / m³. 3 The tar content was reduced to 0.42 g / m³. 3 Without pre-modification, the large molecular humic substances in the leachate cannot be effectively decomposed, resulting in the generation of a large amount of tar during pyrolysis and a reduction in the calorific value of the fuel gas.

[0038] As shown in Table 1, the calorific value of the gas in all embodiments of the present invention is >15 MJ / m³. 3 Example 7 achieved 17.1 MJ / m3 Compared with Comparative Example 1, which directly reinjected the original leachate, the calorific value of the fuel gas increased by 74.7%-96.6%. The reasons for this were analyzed as follows: First, the pre-modified small-molecule organic matter underwent steam reforming and dry reforming reactions in the pyrolysis zone, significantly increasing the production of H2 and CO; second, the reinjected lanthanum-iron co-modified catalyst catalyzed the cracking of tar into small-molecule combustible gases; and third, the organic matter in the leachate served as supplementary fuel, improving the system's energy utilization rate.

[0039] As shown in Table 1, the tar content in all embodiments of the present invention is <0.5 g / m³. 3 In Example 7, the concentration was as low as 0.37 g / m³. 3 Compared with Comparative Example 1, the tar content was reduced by 92.5%-93.4%. This achieved dual removal of tar through source control and process catalysis: firstly, source control, by decomposing large molecular humic substances in the leachate into small molecular organic matter through heterogeneous Fenton pre-modification, thus reducing tar generation at the source; secondly, process catalysis, by using a re-sprayed lanthanum-iron co-modified catalyst in the high-temperature environment of the pyrolysis zone to catalyze the cracking, reforming, and hydrogenation reactions of tar, especially demonstrating excellent removal effects on recalcitrant polycyclic aromatic hydrocarbons.

[0040] As shown in Table 1, the pyrolysis efficiency of Example 1 of the present invention reached 78.9%. The slag loss on ignition of all examples of the present invention was ≤3%, with Example 7 as low as 1.9%. The improvement in pyrolysis efficiency is mainly due to the high gasification efficiency of small molecule organic matter in the pre-modified leachate, the catalyst catalyzing the tar reforming reaction to improve carbon conversion rate, and the intelligent self-response control system ensuring the stable operation of the pyrolysis process. The reduction in slag loss on ignition indicates that the organic matter is pyrolyzed more completely, and the slag can be directly used to prepare building materials, realizing the full resource utilization of municipal solid waste.

[0041] As shown in Comparative Example 5 in Table 1, when operating with fixed parameters, with the lower calorific value of municipal solid waste fluctuating between 3200-4100 kJ / kg, the calorific value of natural gas fluctuates between 11.2-15.8 MJ / m³. 3 The tar content fluctuates between 0.38 and 1.25 g / m³. 3 The pyrolysis efficiency fluctuated between 65.7% and 76.3%, with an average pyrolysis efficiency of only 71.2%, far lower than the 78.9% in Example 1. It is evident that operating with fixed parameters cannot adapt to the fluctuations in the composition and calorific value of municipal solid waste, leading to unstable system operation, a significant reduction in pyrolysis efficiency, and even problems such as excessive tar content and equipment blockage.

[0042] Comparing the data from Example 8 and Comparative Example 5 in Table 1, it can be seen that after adopting the intelligent self-response control system, the fluctuation range of the gas calorific value was reduced to 15.2-17.1 MJ / m³. 3The tar content fluctuation range narrowed to 0.35-0.58 g / m³. 3 The pyrolysis efficiency fluctuation range was reduced to 76.8%-80.5%, with an average pyrolysis efficiency of 78.6%, an improvement of 10.4% compared to fixed-parameter operation. The intelligent self-response control system can dynamically adjust the operating parameters according to the rules in this invention based on real-time monitoring of the pyrolysis zone temperature, gas calorific value, and tar content, effectively offsetting the impact of fluctuations in the composition and calorific value of municipal solid waste on the pyrolysis process, and significantly improving the stability and pyrolysis efficiency of the system operation.

[0043]

[0044] Table 1. Test results for the examples and comparative examples. Following step S3 of Example 1, only the atomization particle size parameter of the high-pressure atomizing nozzle was changed. The relevant test results are shown in Table 2. It can be seen that when the atomization particle size is in the range of 50-100μm, the calorific value of the gas is >15MJ / m³. 3 Tar content <0.5g / m 3 The temperature fluctuation of the pyrolysis furnace is less than ±15℃, and the equipment blockage frequency is less than 1 time per month. When the atomized particle size is less than 50μm, the droplets are easily carried away by the airflow and cannot fully react in the pyrolysis zone, resulting in an increase in tar content. When the atomized particle size is greater than 100μm, the droplets do not evaporate completely, which will cause the temperature of the pyrolysis furnace to drop sharply, the pyrolysis efficiency to decrease, the tar content to increase significantly, and the equipment blockage frequency to be as high as 7 times per month.

[0045]

[0046] Table 2. Test table on the influence of atomized particle size on pyrolysis effect. The catalyst from Example 1 was washed with water, dried, and reused. Measurements were taken as shown in Table 3. Table 3 shows that after 20 cycles of use, the lanthanum-iron co-modified sludge biochar catalyst prepared in this invention still exhibited a macromolecular humic substance decomposition rate of 86.2% and a fuel gas calorific value of 15.1 MJ / m³. 3 The tar content is 0.57 g / m³. 3 The catalyst activity retention rate reached 82.1%, and the excellent cycle stability of the catalyst is mainly due to: first, the formation of MOC chemical bonds between the metal species and the biochar support, which significantly reduced the leaching rate of metal ions; second, during pyrolysis, the reducing groups on the surface of the biochar can reactivate the deactivated Fe. 3+ Reduced to Fe 2+ First, it enables partial self-repair of catalytic activity; second, the porous structure of biochar can protect internal active sites from the influence of the external environment.

[0047]

[0048] Table 3. Test results of the cyclic performance of lanthanum-iron co-modified sludge biochar catalyst. The above provides a detailed description of a system and method for upgrading gas from leachate pyrolysis in municipal solid waste. As can be seen from the examples and comparative examples, the present invention achieves synergistic effects of harmless treatment of leachate and gas upgrading; the catalyst prepared using residual sludge from urban sewage treatment plants as raw material achieves the circular economy goal of treating waste with waste; the intelligent self-response control system can dynamically adjust operating parameters according to real-time operating conditions to ensure long-term stable operation of the system.

[0049] The preferred embodiments of the present invention have been described in detail above, and are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for upgrading natural gas from leachate pyrolysis in municipal solid waste, characterized in that, The system consists of six parts: a lanthanum-iron co-modified sludge biochar catalyst preparation unit, a leachate heterogeneous Fenton pre-modification unit, a catalytic atomization and re-injection unit, a cascade pyrolysis and gasification unit, a fuel gas deep purification unit, and an intelligent self-response control unit. The lanthanum-iron co-modified sludge biochar catalyst preparation unit is used to prepare porous sludge biochar catalysts supported on lanthanum-iron bimetals. The leachate heterogeneous Fenton pre-modification unit adopts a continuous flow heterogeneous Fenton reactor and uses the lanthanum-iron co-modified sludge biochar as a catalyst to decompose the large molecular humic substances in the leachate into small molecular easily gasifiable organic matter. The catalytic atomization and re-spraying unit atomizes and re-sprays the mixture of pre-modified filtrate and catalyst back into the pyrolysis zone of the pyrolysis furnace. The cascade pyrolysis gasification unit is a vertical fixed-bed pyrolysis furnace, which is divided into a drying zone, a pyrolysis zone and a combustion zone from top to bottom, to realize the cascade pyrolysis gasification of municipal solid waste; The gas deep purification unit sequentially removes dust, tar, acidic gases and fine particulate matter from the crude gas. The intelligent self-response control unit adjusts the pre-modification parameters of the leachate and the catalytic re-injection parameters in real time based on the temperature of the pyrolysis zone and the calorific value and composition of the fuel gas.

2. The municipal solid waste leachate pyrolysis gas upgrading system according to claim 1, characterized in that, The lanthanum-iron co-modified sludge biochar catalyst preparation unit is sequentially connected to a sludge pretreatment device, a KOH activation device, a co-impregnation device, a tubular pyrolysis furnace, and a catalyst storage tank. The KOH activation device is used to prepare a porous sludge biochar carrier, and the co-impregnation device is used to impregnate the porous biochar carrier with a mixed aqueous solution of lanthanum chloride and ferric chloride.

3. The municipal solid waste leachate pyrolysis gas upgrading system according to claim 1, characterized in that, The catalytic atomization back spray unit is connected in sequence to the mixing tank, the high-pressure plunger pump and the high-pressure atomizing nozzle; the high-pressure atomizing nozzle is installed in the middle of the pyrolysis zone of the pyrolysis furnace, and the atomized particle size is controlled at 50-100μm.

4. The system for upgrading municipal solid waste leachate pyrolysis gas as described in claim 1, characterized in that, The furnace sidewall of the stepped pyrolysis gasification unit is equipped with multiple temperature sensors, pressure sensors, and an online gas component monitoring instrument, which are electrically connected to the intelligent self-response control unit. The gas deep purification unit is sequentially connected to a cyclone dust collector, an electrostatic precipitator, an alkaline scrubbing tower, and a dry filter. The intelligent self-response control unit is electrically connected to the control valves of the Fenton reactor dosing pump and the catalytic atomization back spray unit.

5. A method for upgrading municipal solid waste leachate pyrolysis fuel gas based on the system described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Preparation of lanthanum-iron co-modified sludge biochar catalyst: It is prepared by using residual sludge from urban sewage treatment plants as raw material, through KOH activation, co-impregnation with lanthanum chloride and ferric chloride, and high-temperature pyrolysis; S2. Leachate heterogeneous Fenton pre-modification: The pretreated leachate is sent into a continuous flow heterogeneous Fenton reactor, and the lanthanum-iron co-modified sludge biochar catalyst and hydrogen peroxide are added to decompose macromolecular humic substances. S3, Catalytic atomization back spray and pyrolysis gasification: The pre-modified leachate is mixed evenly with the catalyst and atomized back sprayed into the pyrolysis zone of the pyrolysis furnace, where it is pyrolyzed and gasified simultaneously with the municipal solid waste; S4. Deep purification and intelligent control of gas: After deep purification, the crude gas is used to obtain high-value gas. The intelligent self-response control unit adjusts the operating parameters in real time to stabilize the pyrolysis process.

6. The method for upgrading municipal solid waste leachate pyrolysis fuel gas according to claim 5, characterized in that, In step S1, the KOH activation conditions are: a mass ratio of sludge fine powder to KOH of 1:2, and constant temperature of 500℃ for 1 hour under a nitrogen atmosphere; the molar ratio of lanthanum chloride to ferric chloride is 1:(5-20), and the total metal ion concentration is 0.05-0.1 mol / L; the pyrolysis conditions are constant temperature of 700℃ for 2 hours under a nitrogen atmosphere.

7. The method for upgrading municipal solid waste leachate pyrolysis gas as described in claim 5, characterized in that, In step S2, the dosage of the lanthanum-iron co-modified sludge biochar catalyst is 0.8-1.5 g / L, the dosage of hydrogen peroxide is 60-90 mmol / L, the reaction pH is 3.0-3.5, the hydraulic retention time is 1.5-2 h, and the decomposition rate of macromolecular humic substances is ≥90%.

8. The method for upgrading municipal solid waste leachate pyrolysis gas as described in claim 5, characterized in that, In step S3, the mass ratio of the pre-modified leachate to the catalyst is 100:(1-3), and the amount of back spray is 15%-25% of the amount of municipal solid waste fed in.

9. The method for upgrading municipal solid waste leachate pyrolysis fuel gas according to claim 5, characterized in that, In step S4, the specific rules for the intelligent self-response control are as follows: When the temperature in the pyrolysis zone is <650℃, increase the amount of pre-modified leachate re-sprayed by 10%-20%; When the gas heat value < 14 MJ / m 3 When the gas heat value < 14 MJ / m 3 When the gas heat value < 14 MJ / m 3 When the gas heat value < 14 MJ / m 3 When the gas heat value < 14 MJ / m 3 When the gas heat value < 14 MJ / m 3 When the When the tar content in the gas is > 3 g / m 3 When the tar content in the gas is > 3 g / m 3 When the tar content in the gas is > 3 g / m 3 When the tar content in the gas is > 3 g / m 3 When the tar content in the gas is > 3 g / m When the lower heating value of municipal solid waste is <3800kJ / kg, increase the amount of leachate re-spraying to 25%-30%, and at the same time increase the amount of catalyst added by 0.2-0.4g / L.

10. The method for upgrading municipal solid waste leachate pyrolysis fuel gas according to claim 5, characterized in that, The pyrolysis slag has a heat loss rate of ≤3% and can be directly used to prepare building materials; the lanthanum-iron co-modified sludge biochar catalyst can be recycled more than 20 times with an activity retention rate of ≥80%.

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