Heating process for regeneration of old asphalt material fibers

Abstract

The invention provides a heating process for asphalt waste material fiber regeneration. The heating process for fiber regeneration of the old asphalt material comprises the following steps: S1, preheating the old asphalt material containing fibers in a reverse-flow waste heat exchanger to obtain a preheated old material; s2, the preheated old material is placed in a microwave heating cavity to be subjected to double-frequency pulse microwave heating; and S3, while the double-frequency pulse microwave heating is performed, nitrogen containing a silane coupling agent is atomized and introduced into the heating cavity through a gas atomization device, so that the coupling agent is subjected to in-situ hydrolysis and polymerization on the surface of the fiber to form the nano-scale protective coating. According to the heating process for regenerating the old asphalt material fibers, target type heating of the asphalt matrix and the fibers is achieved, the heating efficiency is improved by at least 20%, meanwhile, it is ensured that the old material reaches the regeneration temperature within the shortest time, the process period is remarkably shortened, energy consumption is reduced, and the bonding characteristic of asphalt is recovered; and finally, the high-quality regenerated material with stable performance, crack resistance and durability is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of road engineering materials and recycling technology, in particular to a heating process for asphalt old material fiber regeneration. BACKGROUND

[0002] At present, a large amount of asphalt old material (RAP) generated in the process of highway maintenance and reconstruction has become a research hotspot of asphalt pavement recycling. The existing hot mixing regeneration technology usually heats the RAP to above 150-180℃ first, then mixes in a regenerating agent, reinforcing fibers (such as polypropylene fiber, polyester fiber) and other modifiers, and realizes stirring and mixing through a rotary kiln or a mobile hot regeneration device. This process can restore the bonding performance of aged asphalt to a certain extent, and can improve the high-temperature stability and crack resistance of the regenerated material with the help of fiber materials, and has been applied and promoted in some engineering projects.

[0003] However, the above regeneration process still has many deficiencies: the heating equipment has low thermal efficiency, high energy consumption and long heating period, which is not conducive to continuous production; the fiber is prone to melting, breaking or carbonization under high temperature conditions, which seriously weakens its mechanical enhancement effect. The above defects restrict the wide application of fiber-containing RAP regeneration materials and the reliable guarantee of engineering quality. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a heating process for asphalt old material fiber regeneration, which solves the problem of low efficiency of the heating equipment and the problem of weakening of the mechanical effect of the fiber under high temperature conditions.

[0005] To achieve the above object, the present application is implemented by the following technical scheme: a heating process for asphalt old material fiber regeneration, comprising:

[0006] S1. Preheat the fiber-containing asphalt old material in a counter-flow waste heat exchanger to obtain preheated old material;

[0007] S2. Place the preheated old material in a microwave heating cavity and perform double-frequency pulse microwave heating, wherein the double-frequency pulse microwave heating reaches the regeneration temperature of the old material by alternately applying 915MHz high-frequency power microwave energy and 2.45GHz low-frequency power microwave energy;

[0008] S3. At the same time of the double-frequency pulse microwave heating, introduce nitrogen containing silane coupling agent into the heating cavity through a gas atomization device to make the coupling agent hydrolyze and polymerize in situ on the surface of the fiber to form a nanoscale protective coating;

[0009] S4. When the preheated old material reaches the regeneration temperature, inject a pre-proportioned regenerating agent into the heating cavity through a low-shear stirring unit to restore the bonding performance of the asphalt and maintain the mechanical performance of the fiber.

[0010] Preferably, the preheating temperature in S1 is 90-110℃, the mass ratio of solid material to flue gas is 1:0.15, and the preheating time is 3 minutes.

[0011] Preferably, the thermal efficiency η of the counterflow waste heat exchanger satisfies the following model formula:

[0012]

[0013] wherein m gas is the mass flow of flue gas, c p is the specific heat capacity of flue gas, T in is the flue gas inlet temperature, T out is the flue gas outlet temperature, m f is the fuel mass flow, V f is the low calorific value of fuel.

[0014] Preferably, the dual-frequency pulsed microwave heating frequency is: high-frequency power 1.2-1.5 kW, low-frequency power 0.8-1 kW, and pulse duty cycle 0.2-0.8, and the dual-frequency pulsed microwave heating absorption power P satisfies the following model formula:

[0015]

[0016] wherein ω is the angular frequency, ε0 is the vacuum permittivity, ε" is the dielectric loss factor, E is the electric field intensity in the cavity, and V is the heating cavity volume.

[0017] Preferably, the silane coupling agent is an atomized solution with a mass concentration of 0.2%-1.0%, the nitrogen introduction speed is 8-12 L / min, and the thickness of the nanoscale protective coating is 10-50 nm.

[0018] Preferably, the low-shear stirring unit has a shear rate of 1000 s -1 and a stirring time of 5 minutes, and the regenerant is added in a mass fraction of 5%.

[0019] Preferably, a temperature sensor array is arranged in the heating cavity, and the temperature sensor array adopts PID closed-loop control to adjust the high-frequency power microwave energy and the low-frequency power microwave energy in different zones.

[0020] Preferably, the PID closed-loop control comprises the following steps:

[0021] 8.1. The temperature sensor array continuously collects the temperature of each zone in the heating cavity.

[0022] 8.2. The deviation of the temperature of each zone from the preset target temperature is fed back to the PID controller.

[0023] 8.3. The PID controller generates a power adjustment signal and is used to adjust the high frequency power microwave energy and the low frequency power microwave energy.

[0024] The present application provides a heating process for asphalt old material fiber regeneration. It has the following beneficial effects:

[0025] The heating process for asphalt old material fiber regeneration, through the organic combination of counter-flow waste heat exchanger and double-frequency pulse microwave heating, greatly improves the energy utilization rate of the whole heating process. First, the preheating step utilizes the waste heat of the regeneration equipment exhaust gas to preliminarily heat the old material at a lower temperature, reducing the total energy required for microwave heating; second, the double-frequency pulse microwave heating switches between high frequency and low frequency and adopts duty cycle control to achieve target heating of the asphalt matrix and fiber, improving the heating efficiency by at least 20%, while ensuring that the old material reaches the regeneration temperature in the shortest time, significantly shortening the process cycle and saving energy consumption.

[0026] The present technical solution realizes in-situ surface passivation of the fiber and mild repair of the asphalt matrix by introducing a silane coupling agent gas-phase coupling passivation and low-shear regenerant mixing during the heating process. The coupling agent forms a nanoscale protective coating on the fiber surface, effectively inhibiting chain scission and carbonization under high temperature conditions, maintaining the mechanical properties of the reinforcing fiber; low-shear stirring further avoids fiber agglomeration and enables the regenerant and old material to fully integrate, restoring the bonding properties of the asphalt, and ultimately obtaining high-quality regenerated material with stable performance and crack resistance. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flowchart illustrating the implementation of the present application. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] Embodiment One

[0030] As shown in Figure 1 The present application provides a heating process for asphalt old material fiber regeneration, which comprises: S1. Preheating the asphalt old material containing fiber in a counter-flow waste heat exchanger to obtain preheated old material. The preheating temperature is 90-110℃, the mass ratio of solid material to flue gas is 1:0.15, and the preheating time is 3 minutes.

[0031] The heat efficiency η of the counter-flow waste heat exchanger satisfies the following model formula:

[0032]

[0033] wherein, m gas is the flue gas mass flow rate, c p is the flue gas specific heat capacity, T in is the flue gas inlet temperature, T out is the flue gas outlet temperature, m f is the fuel mass flow rate, V f is the fuel low calorific value.

[0034] The specific implementation is as follows:

[0035] 1. Equipment and materials

[0036] Counterflow heat exchanger: The heat exchanger adopts a finned tube design, the inner tube material is high chromium heat-resistant steel, and the shell is carbon steel, which is treated by corrosion-resistant spraying.

[0037] Asphalt old material: RAP from demolished road sections, containing 0.3% (mass fraction) polypropylene fibers, moisture content ≤0.5%, and average particle diameter 4mm.

[0038] Flue gas source: generated by the regenerator unit burning natural gas, inlet temperature about 500℃, dust content ≤50mg / m 3 .

[0039] 2. Process parameter settings

[0040] Old material feeding rate: 1000kg / h, realized by electronic scale and variable frequency feeder to achieve stable feeding.

[0041] Flue gas introduction rate: 150kg / h, monitored in real time by vortex flowmeter to ensure that the solid material: flue gas mass ratio is maintained at 1:0.15.

[0042] Preheating temperature: controlled at 100℃, the old material temperature is monitored by the thermocouple array arranged at the outlet, and the flue gas flow is automatically adjusted by the valve controlled by PLC.

[0043] Preheating time: about 3min, optimized by field test combining the length of the heat exchanger and the residence time of the material layer.

[0044] 3. Process implementation flow

[0045] When starting, first clean and purge the heat exchanger circulation system, and preheat to above 200℃.

[0046] Gradually open the flue gas valve to introduce 500℃ high-temperature flue gas, and start the feeder at the same time to stabilize the feeding rate at 1000kg / h.

[0047] Inside the heat exchanger, the old material and flue gas cross flow in counter flow state. The temperature of the old material is rapidly increased from room temperature to about 100℃, and then the old material is continuously sent out by the screw conveyor.

[0048] After the outlet flue gas temperature is reduced from 500℃ to about 200℃, it is discharged after bag dust removal and flue gas cooling.

[0049] 4. Effect evaluation

[0050] Significant energy-saving effect: The actual thermal efficiency of the heat exchanger is 62% measured by the energy metering device during 8h continuous operation on site, which is about 25% higher than that of the standard dry hot mixing equipment without waste heat recovery.

[0051] Temperature control accuracy: The temperature fluctuation of the material outlet is within ±3℃, which fully meets the pre-treatment requirements of the subsequent double-frequency microwave heating.

[0052] Continuous and stable production: The automatic closed-loop control of the feeding and flue gas flow realizes the increase of the solid material from room temperature to 100℃ within 3min, providing stable and high-temperature uniform preheated old material for the downstream process.

[0053] S2. The preheated old material is placed in the microwave heating cavity for double-frequency pulse microwave heating. The double-frequency pulse microwave heating makes the old material reach the regeneration temperature by alternately applying 915MHz high-frequency power microwave energy and 2.45GHz low-frequency power microwave energy.

[0054] The double-frequency pulse microwave heating frequency is: high-frequency power 1.2kW-1.5kW, low-frequency power 0.8kW-1kW, pulse duty cycle 0.2-0.8, and the double-frequency pulse microwave heating absorption power P satisfies the following model formula:

[0055]

[0056] In the formula, ω is the angular frequency, ε0 is the vacuum dielectric constant, ε" is the dielectric loss factor, E is the electric field intensity in the cavity, and V is the heating cavity volume.

[0057] The specific implementation is as follows:

[0058] Microwave equipment and parameters:

[0059] 2.45GHz high-frequency microwave output power is set to 1.3kW.

[0060] 915MHz low-frequency microwave output power is set to 0.9kW.

[0061] The pulse duty cycle is set to 50%(i.e. heating for 30s and stopping for 30s).

[0062] The total heating time is set to 4min.

[0063] Heating process:

[0064] High and low frequency dual-frequency microwaves are started and output in a duty cycle of 30s on / 30s off.

[0065] The old material continuously turns over in the heating cavity, ensuring that each particle is uniformly heated.

[0066] After 4 minutes, the thermocouple in the cavity shows that the average temperature of the old material reaches 145±3℃, reaching a regenerative temperature range that is sufficient to activate aged asphalt without excessive thermal degradation of the fibers.

[0067] Effect evaluation:

[0068] Heating speed: It only takes 4 minutes to rise from 100℃ to 145℃, saving about 33% compared to traditional continuous single-frequency heating (6 minutes).

[0069] Energy consumption level: The actual measured microwave energy consumption is about 0.08kWh / kg of old material, saving about 20% compared to single-frequency continuous heating.

[0070] Fiber mechanics retention rate: The tensile strength retention rate of polypropylene fibers after heating is 95%, indicating that the pulse dual-frequency mode effectively reduces the thermal damage to the fibers.

[0071] S3. While heating with dual-frequency pulse microwaves, introduce nitrogen containing silane coupling agent into the heating cavity through a gas atomization device, allowing the coupling agent to hydrolyze and polymerize in situ on the fiber surface to form a nanoscale protective coating. The silane coupling agent is an atomized solution with a mass concentration of 0.2% to 1.0%, the nitrogen introduction speed is 8L / min to 12L / min, and the thickness of the nanoscale protective coating is 10nm to 50nm.

[0072] S4. When the preheated old material reaches the regeneration temperature, inject a pre-proportioned regenerating agent into the heating cavity through a low-shear stirring unit to restore the asphalt binding performance and maintain the fiber mechanics performance.

[0073] The low-shear stirring unit has a shear rate of 1000s -1 , the stirring time is 5 minutes, and the mass fraction of the regenerating agent added is 5%. A temperature sensor array is arranged in the heating cavity, and the temperature sensor array uses PID closed-loop control to adjust the high-frequency power microwave energy and the low-frequency power microwave energy in different zones.

[0074] The PID closed-loop control includes the following steps:

[0075] 8.1. The temperature sensor array continuously collects the temperature of each zone in the heating cavity.

[0076] 8.2. The deviation of each zone temperature from the preset target temperature is fed back to the PID controller.

[0077] 8.3. The PID controller generates a power adjustment signal and is used to adjust the high frequency power microwave energy and the low frequency power microwave energy.

[0078] DETAILED DESCRIPTION

[0079] Application scenario: normal working condition, this embodiment takes 1t of asphalt old material containing 0.3% polypropylene fiber as the object to verify the process performance of the application under normal production conditions.

[0080] Equipment and arrangement:

[0081] The preheating section uses a finned tube type counterflow waste heat exchanger with a tube diameter of 50mm and a length of 3m, and the material is high chromium heat-resistant steel.

[0082] Three heating zones are arranged in the microwave heating cavity, and each zone is equipped with a K-type thermocouple.

[0083] The gas atomizing nozzle selects a stainless steel fiber atomizer with a diameter of 0.3mm.

[0084] The stirring unit is a screw type low shear stirrer with adjustable shear rate.

[0085] Process parameters:

[0086] Preheating stage: old material flow rate 1000kg / h, flue gas flow rate 150kg / h, preheating temperature controlled at 100±2℃, residence time 3min.

[0087] Dual-frequency heating: 915MHz power 0.9kW, 2.45GHz power 1.3kW, duty cycle 50%, total heating duration 4min.

[0088] Passivation stage: nitrogen flow rate 10L / min, silane coupling agent concentration 0.5%, forming a nano coating of about 20nm thick on the surface of the fiber.

[0089] Regeneration agent mixing: low shear rate 1000s -1 , stirring for 5min, regeneration agent mass fraction 5%.

[0090] Process control and monitoring:

[0091] The PLC collects the inlet and outlet temperatures of the preheating section in real time and automatically adjusts the flue gas flow rate to maintain a constant preheating temperature difference.

[0092] The microwave cavity is driven by a PID closed-loop controller, and the thermocouple data is updated every 5s to ensure that the temperature deviation of each zone is ≤±2℃.

[0093] The gas atomizing nozzle and the stirrer are linked, and the coupling agent spraying is automatically started when the temperature reaches 140℃.

[0094] Performance evaluation:

[0095] Heating efficiency: preheating + microwave energy consumption 0.08 kWh / kg, overall energy consumption reduced by 22% compared with traditional process.

[0096] Temperature uniformity: temperature difference between sample center and edge after microwave heating <3℃.

[0097] Fiber retention rate: tensile test showed that the fiber strength retention rate was 95%.

[0098] Regenerated material performance: bonding strength reached 1.8 MPa, bending stress increased by 12% in room temperature bending test.

[0099] Example Two

[0100] Different from Example One, the application scenario of this example is high fiber content mode.

[0101] Application scenario: To adapt to the processing of old materials containing 0.5% fiber, the process is adjusted to improve heating uniformity and coating quality.

[0102] Equipment and arrangement:

[0103] Four-hole side-spray atomizing nozzles are added to the microwave cavity, with a nozzle spacing of 300 mm.

[0104] The preheater insulation layer is thickened to 50 mm to reduce heat exchange loss.

[0105] The stirrer is replaced with a low-shear mixer with flexible blades.

[0106] Process parameters:

[0107] Preheating stage: old material flow rate 800 kg / h, flue gas flow rate 120 kg / h, temperature maintained at 105±3℃, residence time 3.5 min.

[0108] Dual-frequency heating: 915 MHz power 1.0 kW, 2.45 GHz power 1.4 kW, duty cycle 60%, heating time 5 min.

[0109] Passivation stage: nitrogen flow rate 12 L / min, coupling agent concentration 0.8%, coating thickness about 35 nm.

[0110] Regenerant mixing: shear rate 1000 s -1 , stirring time 6 min, regenerant 6%.

[0111] Process control and monitoring:

[0112] Dual monitoring of infrared temperature measurement and thermocouple is adopted to realize temperature redundant collection.

[0113] PID parameters are adjusted to K p =0.8, Ki = 0.15, K_d = 0.03, dynamic partitioning of high and low frequency power for fine tuning.

[0114] When any zone temperature deviation exceeds ± 3°C, the system automatically adjusts the duty cycle and aerosolization rate.

[0115] Performance evaluation:

[0116] Heating efficiency: energy consumption 0.095 kWh / kg, increased by about 18% compared to Example A, but still 15% more energy-efficient than single-frequency process.

[0117] Coating quality: SEM observation shows that the nano-passivation coating uniformly covers the fiber surface without obvious cracks.

[0118] Fiber retention rate: tensile strength retention rate 93%.

[0119] Regeneration performance: average life of anti-cracking life test increased by 18%, bonding strength 2.0 MPa.

[0120] Example three

[0121] Unlike Example One, this example applies to high-capacity mode.

[0122] Application scenario: for continuous large-scale production day and night, optimize heating rate and equipment automation level.

[0123] Equipment and arrangement:

[0124] Microwave cavity outer wall is equipped with ultrasonic vibrator (frequency 25 kHz), which promotes the adhesion of coating and fiber.

[0125] An electrostatic precipitator is added at the top of the preheater to reduce dust accumulation.

[0126] The stirrer is replaced with a multi-axis flexible blade design to achieve multi-point interactive shearing.

[0127] Process parameters:

[0128] Preheating stage: old material 1200 kg / h, flue gas 100 kg / h, temperature 90±4°C, residence time 2.5 min.

[0129] Dual-frequency heating: 915 MHz power 0.8 kW, 2.45 GHz power 1.2 kW, duty cycle 40%, heating time 3 min.

[0130] Passivation stage: nitrogen 8 L / min, coupling agent 0.3%, coating about 15 nm.

[0131] Regeneration agent mixing: shear rate 1200 s -1 , stirring for 4 min, regeneration agent 4.5%.

[0132] Process control and monitoring:

[0133] Sensor array increased to 5 groups (thermocouple + infrared combination), real-time monitoring of temperature and surface radiation intensity.

[0134] Improved PID parameters: K p = 1.0, K i = 0.1, K_d = 0.02, to ensure that the temperature difference of each partition is ≤ ± 4℃.

[0135] Ultrasonic vibration is automatically turned on / off according to the progress of coating formation, realizing online optimization of coating quality.

[0136] Performance evaluation:

[0137] Daily production capacity: increased by 30% compared to Example A, reaching 1300 kg / h.

[0138] Energy consumption level: overall energy consumption is 0.07 kWh / kg, which is 15% lower than Example A.

[0139] Coating and fiber performance: the coating is firmly bonded, and the retention rate of fiber tensile strength is 92%.

[0140] Performance of recycled materials: room temperature bonding strength is 1.7 MPa, and long-term weather resistance test shows that the performance attenuation rate is < 5%.

[0141] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A heating process for regenerating asphalt waste fiber, characterized in that: include: S1. The fiber-containing asphalt waste material is preheated in a countercurrent waste heat exchanger to obtain preheated waste material; S2. The preheated old material is placed in a microwave heating cavity for dual-frequency pulse microwave heating, wherein the dual-frequency pulse microwave heating is performed by alternately applying 915MHz high-frequency power microwave energy and 2.45GHz low-frequency power microwave energy to the old material to reach the regeneration temperature; S3. While the dual-frequency pulse microwave heating is being performed, nitrogen containing a silane coupling agent is introduced into the heating cavity by an atomizing device, so that the coupling agent is hydrolyzed in situ on the fiber surface and polymerized to form a nanoscale protective coating; S4. When the preheated old material reaches the regeneration temperature, a pre-proportioned regeneration agent is sprayed into the heating chamber through a low shear stirring unit.

2. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: The preheating temperature in S1 is 90° C. to 110° C., the mass ratio of solid material to flue gas is 1:0.15, and the preheating time is 3 minutes.

3. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: The thermal efficiency η of the counter-flow waste heat exchanger satisfies the following model formula: Among them, m gas is the flue gas mass flow rate, c p is the specific heat capacity of flue gas, T in is the flue gas inlet temperature, T out is the flue gas outlet temperature, m f is the fuel mass flow rate, V f It is the lower calorific value of fuel.

4. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: The dual-frequency pulse microwave heating frequency is: high-frequency power 1.2kW-1.5kW, low-frequency power 0.8kW-1kW, pulse duty cycle 0.2-0.8, and the dual-frequency pulse microwave heating absorption power P satisfies the following model formula: Where ω is the angular frequency, ε0 ​​is the vacuum dielectric constant, ε″ is the dielectric loss factor, E is the electric field intensity in the cavity, and V is the volume of the heating cavity.

5. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: The silane coupling agent is an atomized solution with a mass concentration of 0.2% to 1.0%, the nitrogen introduction speed is 8L / min to 12L / min, and the thickness of the nano-scale protective coating is 10nm to 50nm.

6. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: The shear rate of the low shear stirring unit is 1000s -1 , the stirring time is 5 minutes, and the mass fraction of the regeneration agent added is 5%.

7. The heating process for regenerating asphalt waste fiber according to claim 1, characterized in that: A temperature sensor array is arranged in the heating cavity, and the temperature sensor array adopts PID closed-loop control to perform zone-by-zone regulation on the high-frequency power microwave energy and the low-frequency power microwave energy.

8. The heating process for regenerating asphalt waste fiber according to claim 7 is characterized in that: the PID closed loop control The following steps are involved: 8.

1. The temperature sensor array continuously collects the temperature of each zone in the heating chamber; 8.

2. Feedback the deviation between the temperature of each zone and the preset target temperature to the PID controller; 8.

3. The PID controller generates a power adjustment signal and is used to adjust the high-frequency power microwave energy and the low-frequency power microwave energy.

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