A method for high-temperature pyrolysis of municipal sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas

Abstract

This invention proposes a method for the co-production of high-grade bio-oil and hydrogen-rich fuel gas through high-temperature pyrolysis of municipal sludge, belonging to the field of high-temperature biomass decomposition or gasification. This invention decouples the sludge drying heat source from the pyrolysis process, using steam as the drying heat source to eliminate pre-contamination by tar. The high-temperature tail gas from the pyrolysis reactor outlet is entirely and unidirectionally introduced into a gradient condensation system via an electrically heated pipeline, preventing recirculation back to the drying equipment and avoiding tar condensation and coking. Simultaneously, the dried sludge is pulverized and mixed with an industrial solid waste catalyst, and then subjected to programmed temperature pyrolysis under nitrogen protection. After primary and secondary condensation, the pyrolysis gas undergoes liquid-phase static dehydration to obtain high-grade bio-oil, while the non-condensable gas is separated by a pressure swing adsorption (PSA) system to obtain hydrogen-rich fuel gas. This invention achieves simultaneous and stable co-production of two high-value-added energy products with high purity and high yield, making it suitable for municipal sludge resource utilization, high-quality bio-oil production, and hydrogen-rich fuel gas preparation.

Description

Technical Field

[0001] This invention relates to the field of high-temperature biomass decomposition or gasification, specifically to a method for the co-production of high-grade bio-oil and hydrogen-rich fuel gas through high-temperature pyrolysis of municipal sludge. Background Technology

[0002] Currently, municipal sludge pyrolysis technology mainly focuses on volume reduction and energy recovery, but it generally suffers from problems such as high tar content in the products, poor quality of bio-oil, and difficulty in purifying hydrogen-rich fuel gas. Existing studies mostly adopt pyrolysis gas recirculation drying or combustion reuse methods to pursue system self-heating balance, which leads to heavy tar condensation clogging the equipment, high-value components being burned, making it difficult to simultaneously produce high-grade bio-oil and high-purity hydrogen-rich fuel gas, and resulting in insufficient conversion of sludge organic matter.

[0003] To address these issues, CN115216346B discloses a method and system for preparing hydrogen-rich fuel gas from organic solid waste. This method involves drying the organic solid waste to a water content below 30%, then introducing a gasifying agent and steam into a gasifier at temperatures above 800°C. The flue gas reacts with water to generate hydrogen-rich fuel gas with a hydrogen content of 40%–60%. The waste heat from the high-temperature fuel gas is used to generate steam for reuse. However, while the high-temperature gasification process suppresses tar, it does not provide targeted catalytic control of the cracking pathway, resulting in the fuel gas still containing a significant amount of CO2 and N2, limiting hydrogen purity. Furthermore, the drying section is not completely decoupled from the pyrolysis gas, posing a potential pollution risk of pyrolysis products mixing into the drying system. CN119685046A discloses a method for producing bio-oil through the co-hydrothermal liquefaction of municipal sludge and waste plastics. The method involves mixing municipal sludge and waste plastics, adding Na2CO3 and Co-Mo catalysts, and then carrying out a hydrothermal liquefaction reaction. Bio-oil is obtained through solid-liquid separation, oil-water separation, and supercritical CO2 extraction. However, this method can only produce bio-oil and cannot simultaneously produce high-quality hydrogen-rich fuel gas. Furthermore, the high reaction pressure of hydrothermal liquefaction increases the process cost. At the same time, the problem of directional conversion of the original tar precursors in the sludge has not been solved.

[0004] In summary, existing technologies still cannot resolve the core contradiction between tar pollution and low-value products during sludge pyrolysis. There is an urgent need to develop a method for the high-temperature pyrolysis of municipal sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas. This method should utilize decoupling of the drying heat source, full-volume directional transportation, catalytic pyrolysis, and gradient condensation. Pressure swing adsorption (PSA) combined with other methods enables the high-value conversion of organic matter in sludge. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a method for the co-production of high-grade bio-oil and hydrogen-rich fuel gas through high-temperature pyrolysis of municipal sludge. This invention decouples the sludge drying heat source from the pyrolysis process, using steam as the drying heat source to eliminate pre-contamination by tar. The high-temperature exhaust gas from the pyrolysis reactor outlet is entirely and unidirectionally introduced into a gradient condensation system via an electrically heated pipeline, preventing recirculation back to the drying equipment and avoiding tar condensation and coking. Simultaneously, the dried sludge is pulverized and mixed with an industrial solid waste catalyst, and then pyrolyzed under nitrogen protection with programmed temperature increases. The pyrolysis gas undergoes primary and secondary condensation, followed by liquid-phase dehydration to obtain high-grade bio-oil. The non-condensable gas is separated using a pressure swing adsorption (PSA) system to obtain hydrogen-rich fuel gas. This invention solves the technical problems of high tar content, poor quality and low purity of bio-oil, difficulty in purifying hydrogen-rich fuel gas with insufficient component purity, and incomplete conversion of sludge organic matter in traditional sludge pyrolysis for bio-oil and hydrogen-rich fuel gas production.

[0006] This invention proposes a method for the high-temperature pyrolysis of municipal sewage sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas, such as... Figure 1 As shown, the specific technical solution is as follows:

[0007] Step 1: The municipal sludge in the sludge collection bin is pumped into a low-pressure plate and frame dewatering machine for pre-dewatering. The pre-dewatered sludge is then sent to a disc dryer and dried using steam as a heat source to obtain dried sludge.

[0008] Step 2: After the dried sludge is crushed, it is mixed evenly with the industrial solid waste catalyst. Then the mixture is fed into the tubular furnace, the flanges at both ends are sealed, and the air in the furnace is purged with nitrogen. Then the program is started to heat up the tubular furnace and keep it at the temperature.

[0009] Step 3: Turn on the electric auxiliary heating of the pipeline connecting the exhaust port of the tubular furnace and the condenser, and turn on the gradient condensation system of the condenser to transport the pyrolysis gas in the tubular furnace to the gradient condensation system along the pipeline with electric auxiliary heating.

[0010] Step 4: Adjust the temperature of the primary and secondary condensers, collect the condensed liquid phase after it has been allowed to stand and dehydrate, which is the high-grade bio-oil required. Introduce the uncondensed gas into the PSA system and collect the gas at the exhaust end, which is the hydrogen-rich fuel gas required.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Using steam as the sole heat source for drying prevents the high-temperature tar-containing exhaust gas generated by the pyrolysis reaction from flowing back to the drying equipment. By decoupling the heat source, the drying process involves only water evaporation and does not contain any tar components generated by pyrolysis. This avoids the condensation and accumulation of tar inside the dryer. Furthermore, the steam originates from the combustion heat generated by the combustible exhaust gas, thus achieving resource recycling.

[0012] 2. Industrial solid waste catalyst is uniformly mixed into the dried sludge and pyrolyzed under nitrogen protection and anaerobic conditions with programmed temperature increase. This promotes in-situ deep breaking of C-C and CH bonds and key reactions such as decarboxylation and decarbonylation, reduces the tendency of large molecular organic matter to transform into heavy tar, and guides the cracking path to evolve towards light aliphatic hydrocarbons, aromatic hydrocarbons and hydrogen-rich gases, making the oil and gas generated by pyrolysis purer.

[0013] 3. A gradient condensation system is used to liquefy the pyrolysis gas in stages. Bio-oil is obtained by condensing the liquid phase, while hydrogen-rich gas is obtained by condensing the gas phase. The pyrolysis oil and gas do not undergo any internal combustion consumption or ineffective circulation in the entire separation and purification process, thereby achieving the synchronous and stable co-production of high-grade bio-oil and hydrogen-rich gas.

[0014] 4. Using the combustible flue gas that has been adsorbed and desorbed by the PSA system as a heat source, it is burned to produce steam. The exhaust gas from this secondary combustion is then purified and discharged into the atmosphere, ensuring zero secondary ecological hazards and deep carbon / sulfur closed loop throughout the entire life cycle of the pyrolysis system. Attached Figure Description

[0015] Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a gas chromatogram of the gas before and after PSA adsorption in Example 1 of the present invention. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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] This invention proposes a method for the high-temperature pyrolysis of municipal sewage sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas. The specific technical solution is as follows: 1. Sludge pre-dewatering and drying Municipal sludge is first pre-dewatered using a plate and frame filter press, then fed into a disc dryer to dry it with steam as a heat source. When municipal sludge is discharged from the wastewater treatment plant, the water exists primarily in three forms: free water between particles, capillary-bound water, and intracellular water. This water significantly affects the pyrolysis efficiency and product quality during subsequent pyrolysis. A low-pressure plate and frame dewatering machine, under the clamping force provided by a hydraulic system, traps solid particles in the filter cloth, while free water is forced through the filter cloth under pressure, thus achieving solid-liquid separation.

[0018] After mechanical filtration, most of the free water in the sludge can be efficiently removed, greatly reducing the volume of the sludge and forming a cake. The cake-shaped sludge is then fed into a disc dryer, and steam is introduced into the hollow disc rotor of the disc dryer as a heat source. The heat is transferred to the external wet sludge through the metal wall. When the wet sludge comes into contact with the heated disc surface, the water absorbs the heat and vaporizes. The generated water vapor escapes from the sludge pores and is discharged by the system.

[0019] Since the steam heat source is supplied independently from the outside and has no gas connection with the subsequent pyrolysis process, only the evaporation and diffusion of water are inside the dryer. No tar-containing gas produced by pyrolysis enters, thus avoiding the tar condensation and pollution chain caused by the pyrolysis gas recirculation and drying in the traditional process. This ensures that the heat exchange surface of the dryer remains clean for a long time and will not reduce the heat transfer efficiency due to tar adhesion.

[0020] 2. Anaerobic catalytic pyrolysis of dried sludge After being pulverized, the dried sludge is mixed with an acid-modified industrial solid waste catalyst and heated in a closed tubular furnace after nitrogen purging, with the temperature maintained at that level. The dried sludge will be in lumps or clusters of varying sizes. Direct pyrolysis will result in inconsistent heat penetration depth, with the outer layer overheating while the inner layer is insufficiently pyrolyzed, leading to a disordered product distribution. Pulverization can significantly reduce the size of the sludge particles and make them more uniform, while increasing the specific surface area per unit mass of sludge. This allows heat to be rapidly and evenly transferred to the core of each particle during subsequent heating, ensuring that the organic matter decomposes on the same timescale.

[0021] Because industrial solid waste is rich in various metal oxides such as Fe2O3, Al2O3, and CaO, it provides abundant Lewis acid sites and redox active centers for organic matter decomposition during pyrolysis. Fe2O3 significantly reduces the activation energy of C / C and CH bond breaking, promoting the deep decomposition of macromolecules into small free radical fragments. Alkaline components such as CaO and Al2O3 partially neutralize acidic intermediates, assisting in decarboxylation and decarbonylation reactions, allowing oxygen-containing functional groups to be preferentially removed in the form of CO2 and CO, reducing the oxygen content of bio-oil, and providing acidic sites to promote secondary olefin decomposition. Some iron oxides are reduced to Fe3O4 or Fe under a reducing atmosphere, further enhancing the adsorption and stabilization of macromolecular free radicals, inhibiting bimolecular condensation, and thus reducing the formation of heavy tar. Furthermore, the industrial solid waste undergoes deep dehydration and drying before mixing, and is mechanically ground to maximize its specific surface area, enabling it to provide more active sites during pyrolysis. The acid-modified catalyst removes free CaO through acid impregnation and increases the specific surface area of ​​the catalyst through etching, thereby enriching iron oxides, aluminum oxides and more stable bound CaO in the catalyst. The effective contact area between the catalyst and the sludge substrate and the reaction activity are also improved.

[0022] Because organic matter at high temperatures preferentially undergoes oxidation and combustion in the presence of oxygen, converting high-value hydrocarbons into CO2 and water, it cannot generate bio-oil and fuel gas. However, under nitrogen protection and programmed heating, the covalent bonds such as protein peptide bonds, polysaccharide glycosidic bonds, and lipid ester bonds in the sludge undergo homolytic cleavage under thermal action, generating a large number of C, H, O, and N free radical fragments. Due to the presence of a catalyst and the control of the heating rate, these free radical fragments are more inclined to undergo β-cleavage, rearrangement, and hydrogen transfer reactions, generating light hydrocarbons of moderate molecular weight and small molecule gases, further reducing the risk of generating heavy tar.

[0023] 3. Electric auxiliary heating for directional transport of pyrolysis gas The electric auxiliary heater is activated on the pipeline between the tubular furnace exhaust port and the condenser, allowing the pyrolysis gas to be transported along this pipeline to the gradient condensation system. The high-temperature mixed oil and gas discharged from the pyrolysis reactor is a complex multi-component system, including permanent gases and a large amount of condensable volatiles. Due to the wide boiling point distribution of these condensable volatiles, if the pipe wall temperature is lower than the dew point temperature of some components after the high-temperature oil and gas is discharged from the pyrolysis furnace, these components will undergo a gas-liquid phase change on the wall surface, condensing into a liquid state or even directly solidifying into solid tar. This condensate deposit has high viscosity and adhesion, adhering firmly to the inner surface of the pipe wall and forming hard coke over time. This reduces the effective flow cross-sectional area of ​​the pipeline and increases flow resistance, while also further lowering the pipe wall temperature, accelerating the condensation of subsequent oil and gas, and ultimately leading to complete pipeline blockage.

[0024] To prevent pipeline blockage, electric auxiliary heating is applied during the transport of the mixed oil and gas to the condenser. This actively maintains the pipe wall temperature at a level higher than the dew point of all condensable components, ensuring the mixed oil and gas remains in a gaseous state before entering the condenser. Simultaneously, the positive pressure maintained inside the tubular furnace provides a pressure gradient that drives the unidirectional flow of oil and gas, ensuring all gases move along the pipeline towards the condenser without backflow, stagnation, or accumulation within the furnace.

[0025] 4. Gradient condensation for collecting bio-oil and PSA for collecting fuel gas The pyrolysis gas is liquefied in stages by adjusting the temperatures of the first and second stage condensers. The liquid phase is then allowed to settle and dehydrate to obtain bio-oil, while the non-condensable gas is collected via a PSA (Power Separator) to obtain hydrogen-rich fuel gas. The two condensers are set with different condensation temperatures, utilizing the differences in the boiling points of the components to achieve a fractionation effect. The first stage condenser is set at a relatively high condensation temperature, causing the high-boiling-point heavy components and some water vapor to reach saturation first, resulting in a gas-liquid phase transition and condensation into a liquid state, which is then collected and discharged. This liquid then enters the lower-temperature second stage condenser, where low-boiling-point light aliphatic hydrocarbons, monocyclic aromatic hydrocarbons, and monophenols—components with high combustion value—are forcibly liquefied and efficiently collected at low temperature, forming a liquid mixture containing high-grade bio-oil. Subsequent settling and dehydration removes the water from the mixture, resulting in high-purity, high-grade bio-oil.

[0026] Because the gases that remain undiluted after two stages of condensation have extremely low boiling points, they cannot be effectively liquefied by further cooling. Therefore, a PSA (Pressure Separation and Adsorption) system is needed to separate the mixed gas phase based on the differences in van der Waals forces or electrostatic forces between different gas molecules and the adsorbent surface. Under pressure, the gas mixture passes through the adsorption bed. Gases with stronger molecular polarity, larger molecular diameter, or higher polarizability are preferentially adsorbed and retained in the bed, while hydrogen, with the smallest molecular diameter and weakest polarity, is hardly adsorbed and quickly passes through the adsorption bed, exiting from the outlet. This process enriches the hydrogen. The gas finally collected from the PSA system outlet is hydrogen-rich fuel gas, which can be co-produced with the previously collected high-grade bio-oil.

[0027] Furthermore, during the depressurization desorption and regeneration stage, the PSA system releases a large amount of highly toxic and greenhouse gases rich in hydrogen sulfide, ammonia, trace heavy metals, and high concentrations of carbon dioxide. These gases are entirely introduced into a dedicated, closed combustion furnace for complete oxidation under controlled combustion ratios. The released heat energy is converted into high-temperature steam required for the sludge drying step via a waste heat boiler. The secondary high-temperature flue gas generated by combustion passes sequentially through a selective non-catalytic reduction denitrification unit and a two-stage alkaline spray desulfurization scrubbing tower. The alkaline absorbent thoroughly neutralizes and removes the generated SO2 and HCl, and significantly reduces NO concentration. This ensures that all indicators of the flue gas ultimately emitted into the atmosphere are far below the stringent thresholds of the National Integrated Emission Standard for Air Pollutants, guaranteeing zero secondary ecological hazards and a deep carbon / sulfur closed loop throughout the entire life cycle of the pyrolysis system.

[0028] The following are some specific embodiments of the present invention. Table 1 shows the raw material information of the reagents used in the embodiments.

[0029] Table 1. Raw Material Information Table.

[0030]

[0031] Example 1 S1: Municipal sludge from the sludge collection bin is pumped into a low-pressure plate and frame dewatering machine at a flow rate of 0.8 m3 / h using a sludge pump. It is pre-dewatered using a pressing pressure of 0.7 MPa. When the sludge moisture content is reduced to 60 wt%, it is sent into a disc dryer. Then, 220℃ steam is introduced into the rotor center shaft of the disc dryer through a pipeline as a heat source. At the same time, the disc rotates at a speed of 4 r / min to dry the sludge. The temperature at the discharge end of the dryer is adjusted to 95℃. The dried sludge is then collected at the discharge port.

[0032] S2: The dried sludge obtained in S1 is crushed into uniform particles with a particle size not exceeding 2 mm. Then, 15 wt% of the dried sludge mass is added to the dehydrated, dried and ground red mud and mixed evenly. The mixture is then loaded into the reaction zone of the tubular pyrolysis furnace. The flanges at both ends of the tubular furnace are sealed. High-purity nitrogen is then introduced into the furnace at a flow rate of 0.5 L / min to purge the air in the furnace for 30 min to replace the air inside the furnace. The pressure valve is adjusted to maintain the pressure inside the furnace at a slightly positive pressure of 150 Pa. Then, the temperature inside the furnace is raised to 550 °C at a heating rate of 20 °C / min and held for 30 min.

[0033] S3: An electric auxiliary heating tape is laid on the gas delivery pipe between the exhaust port of the tubular furnace and the gradient condensation system and wrapped with an insulation layer. The electric auxiliary heating at 350℃ is turned on throughout the pyrolysis process, and the oil-gas mixture after pyrolysis is driven to be transported unidirectionally to the condensation system by the 150Pa micro-positive pressure inside the tubular furnace.

[0034] S4: Set the temperature of the first-stage condenser of the gradient condensation system to 90℃ and the temperature of the second-stage condenser to 5℃. Collect the liquid mixture obtained from the two-stage condensation and transfer it to a separatory funnel. After standing at 25℃ for 30 minutes, discharge the lower aqueous phase through the bottom valve and collect the upper oil phase, which is the desired high-grade bio-oil. Simultaneously, pressurize the uncondensed gas after the two-stage condensation to 0.8MPa and introduce it into a four-tower alternating PSA system. Each adsorption tower is filled sequentially from the bottom inlet upwards with 200mm thick activated alumina, 300mm thick silica gel, 500mm thick activated carbon, and 400mm thick 5A separatory funnel. The sub-sieve collects the gas discharged from the top outlet section of the tower, which is the required hydrogen-rich fuel gas. When the adsorbent in the adsorption tower is saturated, the raw material gas is switched to another regenerated adsorption tower through an automatic switching valve. At the same time, the saturated tower is evacuated and depressurized to -0.08MPa to desorb the adsorbed impurities and discharge them, thus completing the adsorbent regeneration. The exhaust gas discharged after desorption is used as combustible flue gas for combustion. The heat energy of combustion is converted into the steam required by S1 through a waste heat boiler. The secondary flue gas generated by combustion passes through a selective non-catalytic reduction denitrification device and a two-stage alkaline spray desulfurization scrubbing tower in sequence, and then the purified exhaust gas is discharged.

[0035] Example 2 The preparation method according to Example 1 differs in that: S2: Replace red mud with steel slag, and the rest of the steps are the same.

[0036] Example 3 The preparation method according to Example 1 differs in that: S2: Replace red mud with fly ash, and the rest of the steps are the same.

[0037] Example 4 The preparation method according to Example 1 differs in that: S1: The pressing pressure for pre-dehydration is 0.5MPa, the steam heat source temperature is 180℃, and the discharge temperature of the dryer is 80℃; S2: The amount of industrial solid waste catalyst added is 10wt% of the dried sludge, the heating rate is 10℃ / min, the pyrolysis temperature is 500℃, and the holding time is 20min. S3: The electric auxiliary heating temperature is 330℃; S4: The temperature of the first-stage condenser is 80℃, the temperature of the second-stage condenser is 0℃, the PSA adsorption pressure is 0.6MPa, and the remaining steps are the same.

[0038] Example 5 The preparation method according to Example 1 differs in that: S1: The pressing pressure for pre-dehydration is 0.9 MPa, the steam heat source temperature is 240℃, and the discharge temperature of the dryer is 110℃; S2: The amount of industrial solid waste catalyst added is 20wt% of the dried sludge, the heating rate is 30℃ / min, the pyrolysis temperature is 600℃, and the holding time is 40min. S3: The electric auxiliary heating temperature is 400℃; S4: The temperature of the first-stage condenser is 100℃, the temperature of the second-stage condenser is 10℃, the PSA adsorption pressure is 1.0MPa, and the remaining steps are the same.

[0039] Example 6 The preparation method according to Example 1 differs in that: S1: The pressing pressure for pre-dehydration is 0.8 MPa, the steam heat source temperature is 210℃, and the discharge temperature of the dryer is 100℃; S2: The amount of industrial solid waste catalyst added is 12wt% of the dried sludge, the heating rate is 15℃ / min, the pyrolysis temperature is 570℃, and the holding time is 35min. S3: The electric auxiliary heating temperature is 360℃; S4: The temperature of the first-stage condenser is 85℃, the temperature of the second-stage condenser is 8℃, the PSA adsorption pressure is 0.7MPa, and the remaining steps are the same.

[0040] Comparative Example 1 The preparation method according to Example 1 differs in that: S2: Install a diversion device at the outlet of the tubular furnace to guide a portion of the exhaust gas to the disc dryer in S1, where it mixes with steam to serve as a heat source for drying. The remaining steps are the same.

[0041] Comparative Example 2 The preparation method according to Example 1 differs in that: S2: After the dried sludge is crushed, no catalyst is added, and it is directly pyrolyzed. All other steps are the same.

[0042] Comparative Example 3 The preparation method according to Example 1 differs in that: S4: Eliminate the first-stage condenser and use only the second-stage condenser for condensation; the remaining steps are the same.

[0043] Comparative Example 4 The preparation method according to Example 1 differs in that: The PSA system is eliminated, and non-condensable gases are collected directly and used as fuel.

[0044] Experimental Example 1 The oven-dried sludge used before pyrolysis in Examples 1-6 and Comparative Examples 1-4 was weighed and its mass was recorded as m. 泥 After pyrolysis and condensation, the collected oil phase was transferred to a pre-weighed conical flask and weighed. The mass m of the bio-oil was calculated. 油 The bio-oil yield is calculated using the formula: m 油 / m 泥 .

[0045] Take 20 mL of bio-oil samples collected in Examples 1-6 and Comparative Examples 1-4. Set the temperature of the constant temperature water bath to 25°C. Rinse the clean and dry 10 mL specific gravity bottle twice with the bio-oil to be tested. Then fill the bottle with the bio-oil to be tested and place it in the constant temperature water bath for 15 min. After the temperature stabilizes, use filter paper to absorb the overflowing oil, stopper the bottle and wipe the outer wall dry. Weigh the bottle with an electronic balance and calculate its density based on the mass of the bio-oil obtained from the weighing.

[0046] Using a fully automated Ubbelohde capillary viscometer, set the constant temperature water bath to 40°C, take 15 mL of bio-oil samples collected in Examples 1-6 and Comparative Examples 1-4, and inject them into the reservoir tube of the viscometer. After the viscometer is kept at a constant temperature for 20 min, draw the bio-oil up to above the highest mark of the upper reservoir bulb, let the oil droplets fall freely, and record the viscosity of the sample as shown on the viscometer.

[0047] According to GB / T 384-2025 "Determination of Calorific Value of Hydrocarbon Fuels - Oxygen Bomb Calorimeter Method", the water content of the bio-oils prepared in Examples 1-6 and Comparative Examples 1-4 was first determined using a Karl Fischer moisture analyzer. Then, the hydrogen content of the bio-oils was determined using an elemental analyzer. Subsequently, 1.00 g of dehydrated bio-oil sample was weighed and placed in a special crucible. The crucible was placed on the crucible support of the oxygen bomb calorimeter, and the ignition wire was fixed to the crucible support, maintaining a 2-3 mm gap between the ignition wire and the sample. 10.0 mL of distilled water was added to the oxygen bomb cylinder. After tightening the oxygen bomb cap, it was placed on the oxygen filling device. The oxygen cylinder valve was slowly opened, and the oxygen pressure was adjusted to 3.0 MPa. The oxygen filling time was 25 s. The oxygen bomb, after being filled, was placed into the inner cylinder of the calorimeter. The calorimeter cap was closed, and the instrument parameters were adjusted before starting the test. The higher heating value Q measured by the instrument was recorded. 高 According to formula Q 低 =Q 高 The lower heating value of the sample is calculated as -2150×(9×H+W), where H is the H element content of the sample and W is the moisture content of the sample.

[0048] The above data is shown in Table 2.

[0049] Table 2. Data on bio-oil grade indicators collected in the examples and comparative cases.

[0050] As can be seen from Table 2, the bio-oil samples prepared in the examples all have high yield and calorific value, and low density and viscosity, indicating that the examples effectively inhibited the formation of heavy tar and promoted decarboxylation and lightening reactions, thus all exhibiting high-grade characteristics. In Comparative Example 1, the pyrolysis tail gas was recycled to the dryer, and the high-temperature tar-containing gas condensed in the low-temperature drying section. Heavy tar was deposited and mixed with sludge, undergoing disordered cracking again, generating a large amount of carbon deposits and polar impurities, resulting in severe pollution of the liquid phase products. Therefore, the yield and calorific value were extremely low, and the viscosity and density were relatively high. In Comparative Example 2, no catalyst was added, and the decarboxylation and decarbonylation reactions were hindered. Oxygen-containing functional groups and long-chain macromolecules were not effectively broken down, resulting in a high proportion of heavy components in the bio-oil, and the oil was viscous and the calorific value was significantly reduced. In Comparative Example 3, only two-stage condensation was used, which resulted in high-boiling-point heavy components not being staged and directly entering the final bio-oil, causing the oil density and viscosity to increase and the calorific value to decrease. In Comparative Example 4, the PSA system was removed, but the bio-oil collection was not affected, so it was not much different from the examples.

[0051] Experimental Example 2 The oven-dried sludge used before pyrolysis in Examples 1-6 and Comparative Examples 1-4 was weighed and its mass was recorded as m. 泥 All the hydrogen-rich gas discharged from the PSA system outlet is introduced into a wet gas flow meter, and the cumulative gas volume V is recorded. The yield of the hydrogen-rich gas is calculated using the formula: V / m³. 泥.

[0052] A gas chromatograph equipped with a thermal conductivity detector was used. The chromatographic column was a 5A molecular sieve packed column with a column temperature of 50°C, an injection port temperature of 100°C, and a detector temperature of 150°C. High-purity argon was used as the carrier gas at a flow rate of 30 L / min. After establishing a standard curve with standard gases, the hydrogen-rich fuel gas collected in Examples 1-6 and Comparative Examples 1-4 was quantitatively injected through a six-way valve. The volume fraction of H2 in the fuel gas was calculated using a chromatography workstation.

[0053] Based on the volume fraction φi of each combustible component in the hydrogen-rich gas collected in Examples 1-6 and Comparative Examples 1-4 determined by gas chromatography, and according to the lower heating value Qi of each component under standard conditions in GB / T 11062-2020 "Calculation Method of Calorific Value, Density, Relative Density and Wobbe Index of Natural Gas", the lower heating value Q of the mixed gas was calculated according to the formula Q=Σ(φi×Qi).

[0054] The above data is shown in Table 3.

[0055] Table 3. Hydrogen-rich gas quality data collected in the examples and comparative cases.

[0056] As shown in Table 3, the hydrogen-rich fuel gas prepared in the examples all exhibited high yields and H2 volume fractions, as well as high lower heating values. This indicates that the examples effectively promoted the directional conversion of sludge organic matter into hydrogen-rich gas. Simultaneously, the PSA purification process efficiently removed impurities such as CO2 and CH4, thus demonstrating the characteristics of high-purity, high-calorific-value hydrogen-rich fuel gas. In Comparative Example 1, the pyrolysis tail gas recirculation and drying resulted in tar condensation pollution, with a large amount of heavy components and inert products mixed into the pyrolysis gas. Therefore, the fuel gas yield, H2 purity, and calorific value were extremely low. In Comparative Example 2, no catalyst was added, hindering the decarboxylation and decarbonylation reactions, resulting in insufficient hydrogen gas generation and an increased proportion of impurity gases. Consequently, the fuel gas yield, H2 purity, and calorific value were all low. In Comparative Example 3, since only a two-stage condensation process was used, the composition of the fuel gas was not affected, and the fuel gas quality was similar to that of the examples. In Comparative Example 4, the PSA system was omitted, and the non-condensable gas was not purified. Therefore, the H2 volume fraction was significantly reduced, the yield was higher due to no loss, and the calorific value decreased due to impurity dilution.

[0057] Experimental Example 3 Gas samples were taken from both before and after processing by the PSA system in Example 1. The two sets of gas samples were then injected into the injection valve of a precision gas chromatograph for analysis. The detectors were configured with a thermal conductivity detector and a flame ionization detector, with high-purity argon used as the carrier gas in the thermal conductivity detector's detection channel. The injection pressure was 0.8 MPa. The test results are as follows: Figure 2 As shown.

[0058] from Figure 2As can be seen in Figure A, which shows the secondary condensate tail gas before purification in the PSA system, the GC spectrum exhibits a highly complex multi-peak mixture. The spectrum contains a very strong CO2 polar molecule main peak, accompanied by absorption peaks of small molecule alkanes, a CO peak, and an N2 peak resulting from the reaction. This reflects the intense decarboxylation and decarbonylation reactions that occurred in the sludge organic matter during pyrolysis and gasification. Although a significant H2 characteristic peak is observed in the spectrum, its area integral is on a similar order of magnitude to the extremely high CO2 and methane peaks, and it does not dominate, indicating that the calorific value of the pyrolysis crude gas was severely diluted. Figure B shows the chromatogram of the hydrogen-rich gas obtained after purification by the PSA system. It can be seen that the complex chromatographic peaks such as CO2, CO, CH4 and N2 that were originally obvious in the crude gas have almost completely disappeared. During the rapid retention period, a sharp single H2 characteristic main peak with an absolutely dominant peak area and a very symmetrical peak shape appears. This indicates that after the physicochemical interception of the four-layer composite bed of the PSA system, the impurity gas is intercepted and H2 can be rapidly penetrated, finally obtaining high-purity hydrogen-rich gas.

Claims

1. A method for high-temperature pyrolysis of municipal sewage sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas, characterized in that, It is prepared by the following method: S1: The municipal sludge in the sludge collection bin is pumped into a low-pressure plate and frame dewatering machine for pre-dewatering, and then the pre-dewatered sludge is sent into a disc dryer to dry it with steam as a heat source to obtain dried sludge. S2: After the dried sludge is crushed, it is mixed evenly with the acid-modified industrial solid waste catalyst. Then the mixture is fed into the tubular furnace, the flanges at both ends are sealed, and the air in the furnace is purged with nitrogen. Then the program is started to heat up the tubular furnace and keep it at the temperature. S3: Turn on the electric auxiliary heating of the pipeline connecting the exhaust port of the tubular furnace and the condenser, and turn on the gradient condensation system of the condenser to transport the pyrolysis gas in the tubular furnace to the gradient condensation system along the pipeline with electric auxiliary heating. S4: Adjust the temperature of the first-stage condenser and the second-stage condenser, collect the condensed liquid phase after it has been allowed to stand and dehydrate, which is the high-grade bio-oil required. Introduce the uncondensed gas into the pressure swing adsorption system, collect the gas at the exhaust end, which is the hydrogen-rich fuel gas required.

2. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 1, characterized in that: The pressing pressure of the pre-dehydration process in S1 is 0.5~0.9MPa; the steam temperature is 180~240℃; and the discharge end temperature of the disc dryer is 80~140℃.

3. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 1, characterized in that: The acid-modified industrial solid waste catalyst mentioned in S2 is one or more of modified red mud, modified steel slag, and modified fly ash.

4. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 1, characterized in that: The amount of industrial solid waste catalyst added in S2 is 10wt%~20wt% of the dried sludge; the heating rate is 10~30℃ / min; the heating temperature is 500~600℃; and the holding time is 20~40min.

5. The method for high-temperature pyrolysis of municipal sludge to co-produce high-grade bio-oil and hydrogen-rich fuel gas according to claim 1, characterized in that: The electric auxiliary heating temperature of S3 is 330~400℃.

6. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 1, characterized in that: The temperature of the first-stage condenser in S4 is 80~100℃; the temperature of the second-stage condenser is 0~10℃; and the pressure of the pressure swing adsorption is 0.6~1.0MPa.

7. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 1, characterized in that: The pressure swing adsorption system described in S4 is a multi-tower alternating system. When the adsorbent is saturated, the adsorption tower is depressurized to desorb and discharge the adsorbed impurity gas, thereby regenerating the adsorbent.

8. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 7, characterized in that: The adsorbent is a combination of activated alumina, silica gel, activated carbon, and 5A molecular sieve, and the adsorbent is arranged in a layered structure.

9. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 7, characterized in that: After the impurity gas is desorbed and discharged, it is introduced into a combustion furnace for complete combustion, and the heat from the combustion is converted into steam through a waste heat boiler.

10. The method for co-producing high-grade bio-oil and hydrogen-rich fuel gas by high-temperature pyrolysis of municipal sludge according to claim 9, characterized in that: The secondary high-temperature flue gas after complete combustion is discharged after desulfurization, denitrification, and acid neutralization.

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