A solar tower-based landfill pollution gas treatment system and method

Abstract

A solar tower-based landfill pollution gas treatment system and method thereof, the system utilizes a solar tower and a two-stage photocatalytic reactor bed to collect and remove foul-smelling gas and methane in pollution and realize methanol resourceization, and is characterized in that it comprises: an import gas control and collection unit (A), a raw material gas pretreatment unit (B), a methane conversion reaction unit (C), and a product collection unit (D). The application proposes a two-stage temperature control photocatalytic methane resourceization treatment device based on a solar tower photovoltaic-electric heating-storage coupling, aiming to utilize renewable electric energy and photocatalytic technology to cooperate, realize normal temperature pretreatment, efficient light coupling catalysis and methanol direct recovery, can run all-weather and low-energy consumption, and can obtain high value-added products, and meet the on-site and modular application requirements of the landfill.

Description

TECHNICAL FIELD

[0001] The present application relates to a system and a method thereof, in particular to a solar tower-based landfill pollution gas treatment system and a method thereof. BACKGROUND

[0002] In the existing landfill gas generated by landfill fermentation, the content of components such as methane, carbon dioxide, ammonia, hydrogen sulfide is complex, which has a huge risk of greenhouse gas emission and odor pollution. The traditional landfill gas treatment and resource utilization methods mainly include the following:

[0003] 1. Direct combustion or flare incineration

[0004] The landfill gas is purified and used for combustion in a boiler or a generator set, or the methane is directly incinerated by a flare to reduce the greenhouse effect. This method has high requirements for gas purity and flow stability, and it is difficult to continuously operate once the gas amount is insufficient; and the chemical energy cannot be recovered in the combustion process, but only can be converted into carbon dioxide and water, which wastes the available energy, and the equipment operation and maintenance cost is high.

[0005] 2. Biological purification

[0006] The filter bed biological purification is carried out by using methane-oxidizing bacteria (as shown in patents CN201410123456.7 and CN103478912A), which can remove methane and odor components at room temperature. However, the microbial activity is extremely sensitive to temperature, humidity and toxic inhibition components, the biological bed is easy to be blocked, frequent maintenance is needed, the treatment efficiency and stability are limited, and it is not conducive to rapid deployment on site.

[0007] 3. High-temperature catalytic oxidation

[0008] At a high temperature above 300℃, the methane is partially oxidized into carbon dioxide or intermediate products by a tubular catalytic bed (such as CN201610987654.X and CN108765432B). This method can improve the methane removal rate, but has large start-up energy consumption, the catalyst is easy to be poisoned and deactivated, and the selectivity for high-value-added products such as methanol is poor.

[0009] 4. Membrane separation and adsorption

[0010] Zeolite molecular sieve membrane or activated carbon, alumina adsorption bed (such as CN102300859B and CN105482156A) is used to separate carbon dioxide, hydrogen sulfide and other impurities, and relatively pure methane tail gas is obtained for power generation or chemical raw materials. However, the front-end pretreatment equipment has large scale and high investment, and the membrane and adsorbent need to be replaced regularly, which has high operation and maintenance cost.

[0011] In the landfill, the treatment of landfill gas has become a major issue, and the influence of landfill gas on the environment needs to be reduced. The existing technical solutions are:

[0012] I. CN103159580B A method for purifying and concentrating methane in landfill gas Technical solution: This patent adopts a five-step combined process:

[0013] 1. Landfill gas compression (normal pressure → 0.1 MPa → 0.2-2.5 MPa)

[0014] 2. Temperature swing adsorption (TSA) desulfurization

[0015] 3. Sulfur-tolerant catalytic deoxidation

[0016] 4. Deacidification (PSA or low-temperature methanol washing to remove CO2, SO2, H2S)

[0017] 5. Concentration (PSA or low-temperature separation to concentrate CH4 to 95%)

[0018] Disadvantages: The process is too long and complex, with large investment and land occupation; multi-stage compression and low-temperature washing have high energy consumption; and methane is not realized as a resource for methanol, only high-purity methane is produced.

[0019] II. CN101219919B A method for purifying and recovering methane from landfill gas Technical solution: compression desulfurization → PSA removal of VOCs / CO2 / N2 → palladium catalytic deoxidation (microchannel reactor) → isobaric temperature swing drying.

[0020] Disadvantages: It relies on a palladium deoxidation microchannel reactor, which has high manufacturing and maintenance costs; desulfurization and PSA still require complex deoxidation; and it does not involve value-added utilization of methane.

[0021] III. CN101555186A A method for deep purification and preparation of methane from landfill gas Technical solution: multi-stage parallel PSA separation, pre-desulfurization, decarburization, and deep drying to extract methane.

[0022] Disadvantages: It completely relies on adsorption separation, which cannot remove NH3, H2S, and other odor components; the adsorbent needs to be frequently regenerated; and it only produces methane, without producing high-value-added products.

[0023] The above technical solutions mostly adopt the "multi-stage treatment" concept, but they all focus on methane purification and recovery, lacking overall design for simultaneous removal of odor components and conversion of methane to methanol. This invention proposes a two-stage catalytic reaction structure based on this:

[0024] First stage: simultaneous removal of NH3, H2S, and other odor gases at room temperature

[0025] Second stage: selective photo-thermal catalytic oxidation coupling of methane to generate methanol

[0026] And integrated solar tower photovoltaic / wind power, power storage system and electric heating and other multi-energy complementary energy supply system, realizes "efficient removal-low energy consumption-high value-added output-fast deployment" of comprehensive technical breakthrough, and has no conflict with the above-mentioned published patent and literature technical route, has obvious innovation and practical value. SUMMARY

[0027] In order to solve the defects existing in the prior art, the application discloses a landfill pollution gas treatment system based on a solar tower, and the technical scheme is as follows:

[0028] A landfill pollution gas treatment system based on a solar tower, which utilizes a solar tower and a two-stage photocatalytic reaction bed to collect and remove foul-smelling gas and methane in pollution and realize methanol resourceization, characterized in that it comprises:

[0029] An import gas control and collection unit (A): a greenhouse is covered with a high-transmittance (>90%) ETFE film, and a methane concentration sensor is installed; when the methane concentration reaches 4%, the fan and the one-way valve are opened, and the PID algorithm dynamically adjusts the introduced air flow to maintain CH4:O2 at 1:1-1:3, thereby improving the subsequent reaction efficiency and ensuring safety.

[0030] A raw material gas pretreatment unit (B): activated carbon (pore size 2-5 nm) is arranged in layers to adsorb foul-smelling gas, and a TiO2-P25 layer on the first-stage reaction bed photocatalytically decomposes NH3 and H2S under 254 nm UV (10 W / m 2 ) light; the gas residence time is greater than or equal to 30 min, the H2S removal rate is greater than 90%, and the NH3 removal rate is approximately 80%. The fan and the one-way valve are opened, and the gas is directed into the next unit.

[0031] A methane conversion reaction unit (C): an electric heating unit adopts a graphene heating film (response

[0032] <10s, temperature control ±1℃, 80% of the electric energy is supplied by the photovoltaic at the top of the tower (efficiency ≈22%), the peak power density is 2kW / m 2 , and the commonly used power is approximately 1kW / m 2 ) cooperates with PID feedback to maintain the reaction bed temperature. The second-stage reaction bed is designed to be replaceable with three technical paths, which can be selected according to actual conditions:

[0033] 1. MnOx / TiO2 porous spheres: 200 °C, atmospheric pressure, and flowing air are sufficient to activate the MnOx surface oxidative sites while avoiding excessive oxidation of methanol to CO2 or H2O, maintaining high methanol selectivity. Catalyst loading 10 wt%, 5–15 wt% is the optimal interval for active site dispersion and specific surface area retention; too high loading easily leads to MnOx agglomeration, reducing catalytic efficiency. CH4:O2 = 1:2 balances CH4 activation and oxidation, achieving a compromise between high yield and moderate selectivity. 0.8 mmol·g_cat in 1 h reaction -1 ·h -1 Methanol, selectivity ≈40%; the porous structure helps gas–solid interface diffusion, but the deep oxidation of MnOx still causes partial methanol loss.

[0034] The mechanism is as follows: porous TiO2 spheres (BET 180–200 m 2 ·g -1 ) provide abundant pores, enhancing CH4 contact with active oxygen species (O (ads) ); MnOx activates C–H bonds through Mn + / Mn 3+ cycles, but part of the ·CH3 intermediate is further oxidized at high temperature.

[0035] 2. Pd1–Fe1 monatomic MOF film: 25–75 °C, CH4:O2 = 1:1, room temperature to moderate temperature photocatalysis avoids thermal decomposition, and a 1:1 ratio ensures sufficient active oxygen without excess oxygen. Light (AM1.5G simulated sunlight) drives the generation of H2O2 intermediates in the MOF. Under high-throughput experimental conditions, 40 mg of catalyst and a 100 sccm flow rate maintain film permeability and uniformity of light. Methanol yield reaches 13.4 mmol·g_cat in 1 h reaction -1 ·h -1 , selectivity ≈90%. The performance is stable for long-term 210 h continuous reaction.

[0036] The mechanism is as follows: in situ H2O2 generation: Pd1–Fe1 synergistic catalytic configuration promotes O2→H2O2 conversion; gas–solid interface advantage: the “breathable” structure of the MOF film ensures rapid diffusion of CH4 / O2 and rapid desorption of CH3OH, avoiding secondary oxidation. Monatomic sites ensure optimized peripheral electron structure, achieving near-zero byproducts.

[0037] 3. VO2–TiO2 heterojunction nanobelt: 150 °C, atmospheric pressure, and visible light irradiation (LED 20 W / m 2), and the VO2 band gap (≈0.7 eV) and TiO2 heterojunction realize the synergistic enhancement of C-H activation. CH4:O2=1:1, maintain the oxidation activity while controlling the over-oxidation. Catalyst dosage 5 g / L, ensure the appropriate light penetration depth and mass transfer efficiency in the reactor. Reaction for 2 h, 1.2 mmol·g_cat -1 ·h -1 Methanol, selectivity ≈50%. VO2 improves the efficiency of electron-hole separation through thermal induction and photoexcitation, and TiO2 provides a stable carrier. Mechanism supplement:

[0038] VO2 / TiO2 heterojunction forms a built-in electric field at the interface, inducing photoinduced electrons e - to VO2, and holes h + to TiO2, enhancing the activation of CH4 C-H bond; at the same time, LED radiation reduces the frequency of thermal decomposition side reactions.

[0039] Among the three alternative paths, the Pd1-Fe1 single atom MOF film path has the highest methanol yield and nearly ideal selectivity, without the need for external H2O2; MnOx / TiO2 and VO2 / TiO2 paths have the advantages of lower cost or wider spectral response, respectively, which can be used as backup schemes to improve the flexibility and reliability of the system.

[0040] Product collection unit (D): condensation recovery method: using a tower height difference ≥20 m and a low-temperature condenser pre-cooled to ≈40℃, and then deep cooling through a -10℃ micro-channel heat exchanger, ≥85% methanol recovery rate can be achieved. Absorption-desorption method: product vapor enters the absorption tower at room temperature, and is fully contacted with countercurrently input organic amine solvents such as diethanolamine, and methanol is selectively absorbed to form a methanol-rich solution, which is desorbed by heating or reducing pressure to obtain methanol vapor and is condensed and collected, and the absorbent is recycled. Membrane separation method: the product vapor is preliminarily dedusted and pressurized and then enters the hydrophilic / oleophilic composite membrane module, and the methanol selectively permeates through the membrane layer and is cooled and condensed outside the membrane to form a liquid product. The scheme can be reasonably selected according to the site conditions.

[0041] The application also discloses a methane resource processing method based on the above-mentioned system, and the method is characterized in that the method comprises the following steps:

[0042] S0: import gas control: collect landfill gas in a thin film greenhouse, when the methane concentration volume ratio reaches 4%, open the one-way valve and fan at a flow rate of 0.5-1 m 3 / min, and dynamically adjust the air / tail gas ratio through a PID algorithm to maintain CH4:O2 at 1:1-1:3;

[0043] S1: Ambient temperature pretreatment: gas is removed in the activated carbon layer and the TiO2-P25 layer with a residence time of > 30 min for H2S and NH3, respectively, UV irradiance 10 W / m 2 , TiO2 load 20 g / L; removal rates > 90% and 80%, respectively. After treatment, the flow is directed by the fan and the one-way valve to the next unit;

[0044] S2: Photocatalytic conversion: start the photovoltaic + electric heating + power storage system, heat the catalytic bed to the corresponding catalytic temperature, and select one of the following three technical paths according to the actual situation and production needs: for high selectivity requirements, use Pd1-Fe1 / MOF path, with a methanol selectivity of up to 90%; for simple materials, use VO2-TiO2 path, with a methanol yield of 0.8 mmol·g_cat -1 ·h -1 or MnOx / TiO2 path, with a methanol yield

[0045] 1.2 mmol·g_cat -1 ·h -1 ;

[0046] S3: Product collection - condensation recovery method: product vapor is first cooled to ≈ 40°C by a low-temperature condenser in the high-position pre-cooling area, and then deep-cooled by a -10°C micro-channel heat exchanger, achieving ≥ 85% methanol liquid collection, and the uncondensed gas is recycled back to S1; absorption-desorption method: product vapor enters the absorption tower at room temperature and is in full contact with countercurrently input organic amine solvents, methanol is selectively absorbed to form a methanol-rich solution, which is heated or decompressed to desorb methanol vapor and condense and collect, and the absorbent is recycled; membrane separation method: product vapor is first dedusted and pressurized, then enters the hydrophilic / oil-repellent composite membrane module, and methanol selectively permeates through the membrane layer to be cooled and condensed outside the membrane to form liquid products, and the unpermeated gas is separated and recycled back to S1.

[0047] Advantages

[0048] Low energy consumption, zero additional fossil fuels: the photovoltaic components at the top of the tower (efficiency ≈ 22%) are organically combined with the solar tower body power storage system, taking lithium ion batteries as an example, the unit volume energy density ≈ 250 Wh / L, the cycle efficiency ≈ 95%, which provides stable power supply for the electric heating unit and other electric modules, achieving all-weather low energy consumption operation. It provides more than 80% clean electricity for the electric heating unit (graphene electric heating film, peak power density 2 kW / m 2 ) and LED / UV light source (10 W / m 2 ), eliminating the dependence on external fuel and power grid, and controlling the daily power consumption of the whole system to be less than 1.2 kWh, while using the residual heat of the solar tower to stably maintain the temperature of the catalytic bed, achieving all-weather low energy consumption operation.

[0049] High selectivity catalytic conversion: two-stage catalytic structure is adopted, the first stage is activated carbon + TiO2-P25 layer at room temperature to quickly adsorb and photocatalytically remove NH3 and H2S, the bed temperature of the first stage is kept at 25°C, UV 254 nm / 10W / m 2 , and the residence time is ≥30 min to achieve H2S removal of >90% and NH3 removal of ≈80%; the second stage preferentially uses Pd1-Fe1 / MOF membrane catalytic path (AM1.5G light illumination 1000W / m 2 , 40mg, 100sccm, 1h reaction), utilizes Pd1 site to photoreduce O2 to generate H2O2, and Fe1 site to immediately oxidize CH4, with methanol selectivity of ≈90% and space-time yield of 13.4mmol·g_cat -1 ·h -1 , to inhibit the generation of by-products while ensuring efficient conversion.

[0050] All-weather, multi-capability complementary stable operation: the system organically couples photovoltaic power generation with electric heating, wind power generation module and lithium ion energy storage system, and can use battery energy storage to continuously power the catalytic bed on cloudy days or at night; when the wind speed is >4m / s, wind power generation can supplement the insufficient photovoltaic power, and through intelligent energy management system, the energy supply mode is automatically switched to ensure stable operation when landfill gas fluctuates or climate changes. The normal power of the electric heating unit is about 1kW, and the peak value of the graphene heating film is 2kW / m 2 , which is 1m 2 , 1kW here; the total power of the rest of the light sources (UV, LED) is about 0.03kW, and the auxiliary power of the fan is about 0.1kW, and the total power load of the system is about 1.13kW. The lithium ion battery with a rated capacity of 6-8kWh can meet the power supply demand of continuous operation for 72 hours, supporting the stable operation of the system in extreme conditions such as no sunlight or at night.

[0051] Modularization, on-site rapid deployment: each functional unit (thin film greenhouse, A / B / C / D tower section, micro-channel condenser) adopts standardized quick connector and bolt connection design, with a single module processing capacity of 500m 3 / h, and the overall tower structure can be transported in sections and completed on-site assembly and debugging within 48h, suitable for landfill sites of different scales and terrains. The system supports vertical tower arrangement and horizontal series arrangement, which can flexibly adapt to different scales and terrain conditions of the landfill site, effectively reducing transportation cost and operation complexity.

[0052] Environmental governance and resource utilization: the integrated process of the present application "pretreatment -> light / heat catalytic methane coupling -> product collection" can efficiently remove NH3, H2S and other malodorous components, realize selective oxidation of methane into methanol at low temperature by photocatalysis, and efficiently collect, truly combine "pollution control" with "high value-added resource utilization", and significantly improve the economy and sustainability of landfill gas treatment. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 The figure is a schematic diagram of the system structure of the present application. DETAILED DESCRIPTION

[0054] I. Implementation steps and specific process

[0055] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the technical solutions of the present application will be described in detail below with reference to the drawings.

[0056] The present application is a landfill pollution gas treatment system based on a solar tower, which uses a solar tower and a two-stage photocatalytic reactor bed to collect and remove malodorous gases and methane in pollution and realize methanol resource utilization, as shown in Figure 1 The system includes the following units:

[0057] Inlet gas control and collection unit: covered with high-transmittance ETFE film, equipped with a methane concentration sensor; when the methane concentration reaches a certain value, the one-way valve is opened, and the PID algorithm dynamically adjusts the air flow to maintain CH4:O2 at 1:1~1:3; a fan is arranged above the unit to pump the raw gas with adjusted oxygen concentration to the subsequent pretreatment unit, and the outlet of the fan is connected with the inlet of the raw gas pretreatment unit;

[0058] Raw gas pretreatment unit: layered activated carbon adsorbs malodorous gases, and the first-stage reactor bed photocatalyzes ammonia and H2S with titanium dioxide, with a gas residence time of no less than 30 min;

[0059] A fan is arranged above the outlet of the raw gas pretreatment unit to stably send the pretreated gas into the methane conversion reaction unit, and the outlet of the fan is connected with the inlet of the methane conversion reaction unit;

[0060] Methane conversion reaction unit: the electric heating unit uses graphene heating film, cooperates with PID feedback to maintain the reaction temperature, and the second-stage reactor bed photocatalyzes methane to generate methanol;

[0061] Product collection unit: the reaction tail gas is condensed by a low-temperature condenser combined with a heat exchanger, and the methanol is recovered by absorption-desorption or membrane separation method according to the actual situation on site.

[0062] Energy supply system: The photovoltaic components at the top of the tower (efficiency ≈ 22%) are organically combined with the solar tower body power storage system. Taking lithium ion battery as an example, the unit volume energy density ≈ 250 Wh / L, the cycle efficiency ≈ 95%, which provides stable power supply for the electric heating unit and other electric modules, and realizes all-weather low-energy consumption operation. It provides more than 80% clean electricity for the electric heating unit (graphene electric heating film, peak power density 2kW / m 2 ) and LED / UV light source (10W / m 2 ), eliminating the dependence on external fuel and power grid, and controlling the daily power consumption of the whole system within 1.2kWh, while using the residual heat of the solar tower to stably maintain the temperature of the catalytic bed, realizing all-weather low-energy consumption operation.

[0063] Among them, it is more refined as:

[0064] 1. The membrane material used in the import gas control unit is polytetrafluoroethylene (PTFE) film, polyether ether ketone (PEEK) film or silicone rubber film, which is prepared by equal thickness extrusion or lamination process, with a thickness of 50-200μm.

[0065] 2. The first stage reaction bed in the raw gas pretreatment unit removes hydrogen sulfide and ammonia gas under the irradiation of ultraviolet lamp at room temperature and the action of p25 titanium dioxide catalyst; and adsorbs foul-smelling gas with adsorbents such as activated carbon and activated alumina as the core.

[0066] 3. The reaction bed of the methane conversion reaction unit is the second stage reaction bed, which is filled with a methane photocatalytic oxidation coupling catalyst for selectively oxidizing coupling of methane to generate methanol under specific temperature control conditions; the catalyst includes VO2-TiO2 heterojunction nanobelt, MnOx / TiO2 porous sphere catalyst or Pd1-Fe1 single atom MOF film.

[0067] 4. The experimental conditions and results of the three corresponding catalysts are:

[0068] (1) MnOx / TiO2 porous spheres: under the conditions of 200℃, normal pressure, flowing air, catalyst loading 10wt%, CH4:O2=1:2, reaction 1h, 0.8mmol·g_cat -1 ·h -1 of methanol yield, selectivity ≈ 40%;

[0069] (2) Pd1-Fe1 single atom MOF film: under the conditions of 25-75℃, CH4:O2=1:1, light (AM1.5G simulated sunlight), 40mg catalyst, 100sccm flow, 1h reaction, methanol yield reaches 13.4mmol·g_cat -1 ·h -1 , selectivity ≈ 90%;

[0070] (3) VO2–TiO2 heterojunction nanobelt: 5 g / L catalyst, 2 h reaction, 150℃, normal pressure, visible light irradiation (LED 20 W / m 2 ), CH4:O2=1:1, selectivity ≈50%.

[0071] 1.2 mmol·g_cat -1 ·h -1 Methanol, selectivity ≈50%.

[0072] 5. The power generation assembly and the electric heating unit: the power generation assembly includes but is not limited to photovoltaic panel assembly, wind turbine, fuel cell, thermoelectric power generation module, biomass power generation unit; the electric heating unit adopts carbon fiber electrothermal film and is equipped with PID temperature control system or selects graphene heating film or metal foil electrothermal film.

[0073] 6. The one-way valve and the fan: the fan is a corrosion and explosion-proof blower or an explosion-proof axial flow fan; a one-way check valve is arranged between the two-stage reaction bed to prevent gas backflow, which is an electromagnetic check valve, a ball valve check valve or a butterfly valve check valve.

[0074] 7. The power storage module includes but is not limited to lithium ion battery pack, sodium sulfur battery, super capacitor, lead carbon battery or solid state battery system; the power storage module is electrically connected with the power generation assembly, is used for storing the electric energy generated by photovoltaic, wind energy or other energy supply units, and stably supplies power to each power consumption module through the energy management system.

[0075] 8. The low-temperature condenser in the product collection unit is a plate heat exchanger or a spiral pipe condenser; the heat exchanger selects a shell and tube heat exchanger or a microchannel heat exchanger; the absorption-desorption method uses amine or selective organic solvent adsorption to concentrate methanol, and then recovers high-purity methanol through heating or vacuum desorption; the membrane separation method separates the pre-cooled liquid through hydrophilic / lipophilic composite membrane, so that methanol penetrates the membrane and impurities are retained, thereby realizing condensation recovery.

[0076] 9. The specific flow includes the following steps:

[0077] S0: import gas control: collect landfill gas in a thin film greenhouse, when the methane concentration volume ratio reaches 4%, open the one-way valve and the fan at a flow rate of 0.5-1 m 3 / min, and the PID algorithm dynamically adjusts the air / tail gas ratio to maintain CH4:O2 at 1:1-1:3;

[0078] S1: normal temperature pretreatment: the gas stays in the activated carbon layer and the TiO2-P25 layer for ≥30 min to remove H2S and NH3, respectively, and the UV irradiance is 10 W / m 2TiO2loaded 20 g / L; removal rates of >90% and 80%, respectively. After treatment, the flow is directed to the next unit by a fan and a one-way valve;

[0079] S2: Photocatalytic conversion: start photovoltaic + electric heating + power storage system, heat the catalytic bed to the corresponding catalytic temperature, and select one of the following three technical paths according to the actual situation and production needs: for high selectivity requirements, use Pd1-Fe1 / MOF path, with a methanol selectivity of up to 90%; for simple materials, select VO2-TiO2 path, with a methanol yield of 0.8 mmol.g_cat -1 ·h -1 or MnOx / TiO2 path, with a methanol yield of 1.2 mmol.g_cat

[0080] ·h -1 ·h -1 ;

[0081] S3: Product collection—condensation recovery method: product vapor is first reduced to ≈40°C by a low-temperature condenser in a high-position pre-cooling area, and then deep-cooled by a -10°C micro-channel heat exchanger, achieving ≥85% methanol liquid phase collection, and the uncondensed gas is recycled back to S1; absorption-desorption method: product vapor enters the absorption tower at room temperature and is in full contact with countercurrently input organic amine solvents, and methanol is selectively absorbed to form a methanol-rich solution, which is desorbed by heating or reduced pressure to obtain methanol vapor and condense and collect, and the absorbent is recycled; membrane separation method: product vapor is first dedusted and pressurized, and then enters the hydrophilic / oil composite membrane module, and methanol selectively permeates through the membrane layer and is cooled and condensed outside the membrane to form liquid products, and the unpermeated gas is separated and recycled back to S1.

[0082] II. Specific experimental mechanism of malodorous gas pretreatment and methane conversion

[0083] An example of a reaction mechanism for malodorous gas pretreatment is as follows:

[0084] If H2S is completely oxidized to SO4 2- and H2O:

[0085]

[0086] or elemental sulfur and water:

[0087]

[0088] The photocatalytic reaction degradation process of ammonia gas is generally recognized to be completed in multiple steps:

[0089] TiO2+hv→h + +e -

[0090] h ++ H2O → ·OH + H +

[0091] NH3 + ·OH → ·NH2 + H2O

[0092] ·NH2 + O2 → H2NOO·

[0093] H2NOO· + ·OH → H2NOOOH

[0094] H2NOOOH → HNO2 + H2O

[0095] HNO2 + 2·OH → HNO3 + H2O

[0096] Experimental conditions

[0097] Temperature: T = 25°C (room temperature)

[0098] UV light: λ = 254 nm, light intensity I = 10 W·m -2

[0099] TiO2-P25 loading: C = 20 g·L -1 (photocatalytic layer)

[0100] Activated carbon layer: specific surface area ≥ 1000 m 2 ·g -1 , filling volume 20 g·L -1

[0101] Gas residence time: t ≥ 30 min

[0102] Relative humidity: RH ≈ 50%

[0103] Performance indicators

[0104] H2S removal rate: > 90%

[0105] NH3 removal rate: ≈ 80%

[0106] Reasons for parameter selection

[0107] 1. UV wavelength and intensity

[0108] 254 nm corresponds to the TiO2 band width (≈ 3.2 eV), which can efficiently excite electron-hole pairs to generate ·OH and ·O2 - radicals;

[0109] 10 W·m -2 Ensure that sufficient active sites are continuously generated, avoiding both light saturation and energy consumption.

[0110] 2. TiO2-P25 loading

[0111] 20 g·L-1 A uniform and non-overthick catalytic layer can be formed, taking into account the light penetration depth and catalytic site density; the TiO2 surface density is positively correlated with the reaction rate.

[0112] 3. Residence time

[0113] 30 min (1800 s) far exceeds the 120 s required for typical H2S oxidation, which can ensure high removal rate of low concentration (<100 ppmv) H2S and NH3 (<200 ppmv).

[0114] 4. Activated carbon pre-adsorption

[0115] High specific surface area (≥1000 m 2 ·g -1 ) effectively traps organic sulfur and NH3, greatly reducing the pollutant load entering the TiO2 layer, and avoiding early catalyst passivation.

[0116] The mechanism is as follows:

[0117] H2S photocatalytic oxidation

[0118] 1. TiO2 generates e - / h + pairs under UV excitation;

[0119] 2. h + and surface water or OH - generate ·OH, which gradually oxidizes H2S into S 0 → SO3 2- → SO4 2- ;

[0120] 3. SO2 intermediates are extremely low, avoiding secondary gas-phase pollution.

[0121] NH3 photocatalytic oxidation

[0122] 1. h + first oxidizes NH3 into NH2· / NH·, and then ·OH or ·O2 - occurs in a series of radical reactions;

[0123] 2. intermediates NO2 - , NO3 - finally desorb to generate N2, N2O, etc. Inert gas;

[0124] 3. This path avoids the formation of a large amount of NO x , inhibiting secondary pollution.

[0125] Synergistic adsorption-photocatalytic effect: the activated carbon layer first traps macromolecules and easily aggregated pollutants, and releases them uniformly to the downstream photocatalytic layer; moderate humidity maintains the activity of the TiO2 surface, delaying catalyst deactivation.

[0126] Methane conversion:

[0127] 1. MnO x / TiO2 porous spheres

[0128] Experimental conditions

[0129] Temperature: T = 200 °C

[0130] Pressure: P = 1 atm

[0131] Atmosphere: flowing air

[0132] Catalyst loading: 10 wt% MnO x (mass fraction)

[0133] Feed ratio: CH4:O2 = 1:2 (volume ratio)

[0134] Reaction time: t = 1 h

[0135] Performance indicator methanol yield: 0.8 mmol-g_cat -1 ·h -1

[0136] Methanol selectivity: ~40%

[0137] Parameter selection reasons:

[0138] 1. Temperature and pressure: 200 °C can activate Mn 4+ / Mn 3+ oxidation cycle without excessive oxidation of methanol; 1 atm is convenient for device operation.

[0139] 2. Loading: 10 wt% in the range of 5-15 wt% can balance activity site dispersion and specific surface area (BET 180-200 m 2 ·g -1 ), avoiding MnO x agglomeration.

[0140] 3. Gas ratio: CH4:O2 = 1:2 balances C-H bond activation and methanol selectivity, inhibiting CO2 generation.

[0141] Mechanism explanation: porous TiO2 spheres provide abundant gas-solid interfaces, promoting CH4 contact with active oxygen species (O (ads) ); MnO x activates C-H bonds through Mn 4+ / Mn 3+ periodic redox, and the intermediate ·CH3 species is easily further oxidized, leading to decreased selectivity.

[0142] 2. Pd1-Fe1 monatomic MOF membrane

[0143] Experimental conditions

[0144] Temperature range: T = 25-75 °C

[0145] Pressure: P = 1 atm

[0146] Light source: AM1.5G simulated sunlight

[0147] Catalyst dosage: m = 40 mg (thin film form)

[0148] Gas flow rate: Q = 100 sccm

[0149] Feed ratio: CH4:O2=1:1 (volume ratio)

[0150] Reaction time: t = 1 h (long-term stability test t = 210 h)

[0151] Performance indicators

[0152] Methanol yield: 13.4 mmol-g_cat -1 ·h -1

[0153] Methanol selectivity: ≈90%

[0154] Stability: continuous operation for 210 h with no significant performance decay

[0155] Reasons for parameter selection:

[0156] 1. Temperature and light: photocatalysis at 25-75 °C avoids thermal decomposition, and AM1.5G ensures both visible and ultraviolet light.

[0157] 2. Ratio and flow rate: a 1:1 ratio provides sufficient active oxygen, and a flow rate of 150 sccm ensures uniform gas-solid mass transfer and light in the thin film.

[0158] 3. Catalyst form: a 50 mg single-atom Pd-Fe MOF film has a high specific surface area and a "gas-permeable" structure.

[0159] Mechanism explanation:

[0160] Pd1-Fe1 synergistic catalysis generates H2O2 in situ, and CH4 is efficiently oxidized to CH3OH.

[0161] The MOF film structure promotes rapid desorption of intermediate products and inhibits secondary oxidation.

[0162] Single-atom sites ensure optimized peripheral electron structure, achieving near-zero byproducts.

[0163] 3. VO2-TiO2 heterojunction nanobelt

[0164] Experimental conditions:

[0165] Temperature: T = 150 °C

[0166] Pressure: P = 1 atm

[0167] Light source: Visible light LED, irradiation intensity I = 20 W·m -2

[0168] Catalyst concentration: C = 5 g·L -1

[0169] Feed ratio: CH4: O2 = 1:1 (volume ratio)

[0170] Reaction time: t = 2 h

[0171] Performance indicators:

[0172] Methanol yield: 1.2 mmol·g_cat -1 ·h -1

[0173] Methanol selectivity: ≈ 50%

[0174] Reasons for parameter selection:

[0175] 1. Synergy of photo-thermal: 150 °C and 20 W·m -2 Visible light co-activates VO2 (band gap ≈ 0.7 eV) and TiO2, enhancing C–H bond activation;

[0176] 2. Ratio: 1:1 gas ratio balances activity and selectivity;

[0177] 3. Concentration: 5 g·L -1 Ensures balance between light transmission depth and mass transfer efficiency in the reaction medium.

[0178] Mechanism explanation: The VO2 / TiO2 heterojunction interface forms an internal electric field, promoting the migration of photo-generated electrons (e - ) to VO2 and holes (h + ) to TiO2; photo-thermal double excitation and band gap regulation synergistically enhance CH4 C–H bond activation, but some intermediates are still oxidized at high temperatures.

[0179] In summary, the technology of collecting and removing polluted malodorous gases and methane and realizing methanol resourceization based on a solar tower and a two-stage photocatalytic bed realizes the green reuse of landfill gas.

[0180] The application provides a two-stage temperature control photocatalytic methane resource treatment device based on a solar tower photovoltaic-electric heating-electric storage coupling, aiming at realizing normal temperature pretreatment, efficient light coupling catalysis and methanol direct recovery by using renewable electric energy and photocatalysis technology, and meeting on-site and modular application requirements of a landfill site.

[0181] The application provides a landfill site pollution gas treatment system and method based on a solar tower, aiming at realizing green resource utilization of pollution gas.

[0182] I. Multi-energy complementary integrated energy supply system

[0183] All-weather, multi-energy complementary stable operation: the system organically couples photovoltaic power generation and electric heating, a wind power generation module and a lithium ion electric storage system, and can continuously supply power to the catalytic bed by using battery energy storage on cloudy days or at night; when the wind speed is greater than 4 m / s, wind power generation can make up for insufficient photovoltaic power, and the energy supply mode is automatically switched by an intelligent energy management system, so that the system can stably operate when the landfill gas volume fluctuates or the climate suddenly changes. The normal power of the electric heating unit is about 1 kW (the peak value of the graphene heating film is 2 kW / m 2 , and the power is calculated at 1 m 2 ); the total power of the remaining light sources (UV, LED) is about 0.03 kW, the auxiliary power of the fan is about 0.1 kW, and the total power load of the system is about 1.13 kW. The lithium ion battery group with a rated capacity of 6-8 kWh can meet the power supply demand of continuous operation for 72 hours, and support the stable operation of the system in extreme working conditions such as no sunlight or at night.

[0184] II. Two-stage catalytic reaction structure design

[0185] Different from the traditional single gas treatment mode, the application clearly adopts the “two-stage treatment” concept: the first step is a normal temperature pretreatment stage, mainly removing NH3, H2S and other malodorous components in landfill gas; the second step is a methane conversion stage, realizing selective conversion of methane into methanol through parallel catalytic paths.

[0186] 1. Normal temperature pretreatment area:

[0187] After the raw gas is collected, it first enters the room temperature pretreatment unit, and the gas stays for more than 30 seconds under the action of 254 nm ultraviolet lamp irradiation (light intensity 10 W / m 2 ) and P25 type TiO2 catalytic layer (20 g / L load); the upper layer is filled with activated carbon and alumina (20 g / L) to synergistically adsorb H2S and other components. Product analysis shows that the NH3 conversion product is N2 (73.7%), NO3- (23%), NO x (6.3%), H2S conversion products are elemental sulfur, sulfate and sulfite, overall removal rate is about 50-90% within 30 minutes, and the gas basically meets the standard before entering the next catalytic module.

[0188] 2. Methane catalytic conversion stage:

[0189] This stage has three reaction paths to choose from:

[0190] (1) Pd1-Fe1 single atom MOF membrane path (recommended main path):

[0191] Co-localize Pd1 and Fe1 single atom sites (spacing <1 nm) in NH2-UiO-66(Zr) membranes to construct gas-solid confined catalytic interfaces (pore size 0.8-1.2 nm); under AM1.5G sunlight (1000 W / m 2 ) irradiation and 75°C electric heating film heating, in CH4:O2=1:1 atmosphere, flow rate 100 sccm, catalyst 40 mg, reaction for 1 hour, methanol yield increases from 4.4 at room temperature to 13.4 mmol·g_cat -1 ·h -1 , and selectivity ≈90%. Pd1 sites are responsible for reducing O2 to generate H2O2, and Fe1 sites immediately use H2O2 to oxidize CH4 to generate CH3OH, avoiding the addition of H2O2 and liquid dilution, enhancing the methanol desorption rate and catalytic cycle efficiency, which is a key innovation point to realize efficient resource utilization.

[0192] (2) MnOx / TiO2 porous sphere path:

[0193] Under normal pressure air, at 200°C, 5wt% MnOx loaded TiO2 porous spheres (catalyst concentration 5g / L) run for 1 hour, methanol yield is 0.8 mmol·g_cat -1 ·h -1 , selectivity is about 40%. Although the temperature is higher, it is simple in structure and low in cost, and is suitable as a backup path.

[0194] (3) VO2-TiO2 heterojunction nanobelt path:

[0195] VO2 interface modified TiO2 heterojunction, under LED visible light irradiation (20W / m 2 ), CH4:O2=1:1, 1atm oxygen atmosphere, 10g / L catalyst, run for 2 hours, methanol yield is 1.2 mmol·g_cat -1 ·h -1, the selectivity is about 50%. This path has visible light response and high thermal capacity stability, and can be used as a flexible supplement under certain working conditions.

[0196] III. Modular deployment

[0197] The collection unit, pretreatment reaction module, film greenhouse, import control and electric heating device are fast plug-in modular designs, and the processing capacity of a single module can reach 500m 3 / h, which can be expanded in parallel, and the on-site transportation and installation can be completed within 48 hours, which is extremely suitable for landfill site deployment. The system supports vertical tower arrangement and horizontal series arrangement, and can flexibly adapt to landfills of different scales and terrain conditions, effectively reducing transportation costs and operation and maintenance complexity.

[0198] IV. Online closed-loop control and safety protection

[0199] The system is equipped with a PID temperature controller, an online gas chromatography monitoring module, a methane concentration sensor (alarm threshold 1%) and a multi-stage interlocking electromagnetic one-way valve to realize real-time adjustment of temperature, flow and component concentration; the emergency pressure relief valve has a response time of <0.1 seconds, and cooperates with the corrosion and explosion-proof blower to ensure stable and safe system operation.

[0200] In summary, the present application takes a solar tower as the core carrier, integrates photovoltaic, wind energy and power storage technologies, combines two-stage catalytic reaction and high-efficiency condensation path, and first constructs a two-stage temperature-controlled photocatalytic methane resource treatment device based on solar tower photovoltaic-electric heating-power storage coupling.

[0201] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A landfill pollutant gas treatment system based on a solar tower, which utilizes a solar tower and a two-stage photocatalytic reaction bed to collect and remove odorous gases and methane from pollutants and realize methanol resource recovery, characterized by: Imported gas control and collection unit: The shed is covered with a high-transmittance ETFE film and equipped with a methane concentration sensor. When the methane concentration reaches a certain level, the one-way valve is opened in conjunction with the PID algorithm to dynamically adjust the air flow rate and keep the CH4:O2 ratio between 1:1 and 1:

3. A fan is installed above this unit to pump the raw gas with the adjusted oxygen concentration to the subsequent pretreatment unit. The outlet of the fan is connected to the inlet of the raw gas pretreatment unit. Raw material gas pretreatment unit: stratified activated carbon adsorption of odorous gases, titanium dioxide photocatalysis of ammonia and H2S on the first-stage reaction bed, gas residence time ≥30min; A blower is installed above the outlet of the feed gas pretreatment unit to stably send the pretreated gas into the methane conversion reaction unit. The outlet of the blower is connected to the inlet of the methane conversion reaction unit. Methane conversion reaction unit: The electric heating unit uses a graphene heating film, combined with PID feedback, to maintain the reaction temperature. In the second-stage reaction bed, methane is photocatalyzed to produce methanol. Product collection unit: The reaction tail gas is condensed by using a low-temperature condenser and heat exchanger in combination, and methanol is recovered by absorption-desorption or membrane separation method according to the actual site conditions. The low-temperature condenser is a plate heat exchanger or a spiral tube condenser; the heat exchanger is selected as a shell-and-tube heat exchanger or a microchannel heat exchanger; the absorption-desorption method uses amines or selective organic solvents to adsorb concentrated methanol, and then recovers high-purity methanol by heating or vacuum desorption; the membrane separation method separates the pre-cooled liquid through a hydrophilic / lipophilic composite membrane, allowing methanol to permeate through the membrane and impurities to be retained, thereby achieving condensation and recovery. The first-stage reaction bed of the reactor removes hydrogen sulfide and ammonia under the irradiation of room temperature and ultraviolet light and the action of P25 titanium dioxide catalyst. The second-stage reaction bed is filled with a methane photocatalytic oxidation coupling catalyst, which is used to selectively oxidize and couple methane to methanol under specific temperature control conditions. The catalyst includes VO2–TiO2 heterojunction nanoribbons, MnOx / TiO2 porous spherical catalysts or Pd1-Fe1 single-atom MOF membranes.

2. The landfill polluted gas treatment system based on a solar tower according to claim 1, characterized in that, For the second-stage reaction bed to process methane into methanol, one of the following three technologies can be selected based on the actual site conditions and production needs: (1) MnOx / TiO2 porous spheres: Under conditions of 200℃, normal pressure, and flowing air, with a catalyst loading of 10wt% and CH4:O2 = 1:2, 0.8 mmol·g_cat was obtained after 1 h of reaction. -1 ·h -1 Methanol yield, selectivity ≈ 40%; (2) Pd1–Fe1 single-atom MOF membrane: Under the conditions of 25–75℃, CH4:O2=1:1, light irradiation, AM1.5G simulated sunlight, 40mg catalyst, and 100sccm flow rate, the methanol yield reached 13.4mmol·g_cat in 1h reaction. -1 ·h -1 Selectivity ≈ 90%; (3) VO2–TiO2 heterojunction nanoribbons: at 150℃, normal pressure, and LED 20W / m 2 Under visible light irradiation, CH4:O2 = 1:1 conditions, and a catalyst concentration of 5 g / L, 1.2 mmol·g_cat was obtained after a reaction time of 2 h. -1 ·h -1 Methanol, selectivity ≈ 50%.

3. The landfill polluted gas treatment system based on a solar tower according to claim 1, characterized in that, It also includes power generation components and electric heating units. Power generation components include: photovoltaic panel components, wind turbines, fuel cells, thermoelectric power generation modules or biomass power generation units.

4. The landfill polluted gas treatment system based on a solar tower according to claim 1, characterized in that, It also includes energy storage modules, including: lithium-ion battery packs, sodium-sulfur batteries, supercapacitors, lead-carbon batteries or solid-state battery systems; the energy storage modules are electrically connected to the power generation components and are used to store electrical energy generated by photovoltaic, wind power or other power supply units, and to supply stable power to each power consumption module through the energy management system.

5. The landfill polluted gas treatment system based on a solar tower according to claim 1, characterized in that, The gas used in the imported gas control and collection unit is prepared by equal thickness extrusion or lamination process, with a thickness of 50–200 μm.

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