Method for screening and recycling pile foundation mud

Abstract

The application discloses a pile foundation mud screening and recycling method and relates to the technical field of solid waste treatment. The method mainly solves the problems of low solid-liquid separation efficiency, insufficient recovery of useful components and poor performance of regenerated aggregates in traditional pile foundation mud treatment. The technical scheme points of the method comprise the following steps: inputting the pile foundation mud into a high-frequency vibrating screen to separate coarse aggregates, medium particles and primary mud; grading and intercepting fine sand and powder particles from the primary mud and outputting superfine mud; inputting the superfine mud into a slurry storage tank and controlling the viscosity and specific gravity value of the superfine mud according to real-time monitoring; mixing the coarse aggregates, medium particles, fine sand, powder particles and solid cake-shaped substances generated by pressure filtration with aluminate activator and silica ash to form a solid mixture; and finally calcining the solid mixture in a rotary calcining kiln to generate regenerated aggregates. The method is mainly used for efficient resource recycling of abandoned pile foundation mud, and can produce regenerated aggregates which can replace natural aggregates, thereby significantly reducing environmental pollution and resource waste.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology. More specifically, this invention relates to a method for screening and recycling pile foundation slurry. Background Technology

[0002] Waste mud generated during the construction of building pile foundations usually contains a large amount of sand, clay and water, and its efficient recycling faces multiple technical bottlenecks. First, the traditional screening process is not precise enough in separating mud components. Due to the high viscosity and wide particle size distribution (0.1~5 mm) of pile foundation mud, conventional single-layer vibrating screens or fixed aperture screens are prone to the following defects: (1) coarse aggregate (>2 mm) and medium particles (0.5~2 mm) are mixed due to screen hole blockage or adhesion, resulting in a decrease in aggregate recovery rate; (2) fine particles (<0.5 mm) cannot be effectively intercepted and are lost with the mud, causing a burden on subsequent treatment. This problem stems from the non-Newtonian fluid characteristics of mud - viscous resistance makes small-diameter particles easy to adhere to the surface of large particles, while the wide particle size distribution requires multi-stage screening, but existing equipment is difficult to balance separation efficiency and anti-clogging requirements.

[0003] Secondly, the operational stability of the hydrocyclone separator is significantly affected by fluctuations in the solid phase concentration of the slurry. In actual construction, the slurry concentration often varies within the range of 15% to 35%, while the separation efficiency of the hydrocyclone is highly dependent on the inlet pressure. When the solid phase concentration increases, the rheological properties of the slurry change (such as increased viscosity). If a fixed pumping pressure is maintained, it will lead to: (1) blockage of the underflow port when the concentration is >25%, resulting in the failure to retain fine sand (0.18~0.52 mm); (2) "coarse run" of the overflow port when the concentration is <20%, allowing the target powder particles (0.065~0.22 mm) to enter the ultrafine slurry. Historical attempts to solve this problem include manually adjusting the pump pressure or adding a concentration detector, but due to the rapid dynamic changes in slurry concentration (fluctuation of ±5% per minute) and the lag in manual response, it is impossible to achieve real-time matching of pressure and concentration, resulting in a separation efficiency fluctuation of >30%.

[0004] Furthermore, the material circulation during the pressure regulation process causes secondary damage. During the pressure switching stage of the cyclone system (e.g., 0.7→1.3 MPa), if a step pressure change is directly implemented: (1) the sudden pressure change causes the flow field inside the cyclone to become turbulent, and the separated particles are remixed; (2) fine sand and powder particles collide at high speed with the cyclone wall under high pressure difference, resulting in breakage (the particle size <0.1 mm increases by about 15%). Although a buffer bin was used to temporarily store the material, it needs to be pumped again during reprocessing - the high shear force of conventional centrifugal pumps (impeller linear velocity >10m / s) further aggravates particle breakage, resulting in a strength loss of 8%~12% in the recycled aggregate. The root cause of this problem lies in the contradiction between the compressive strength (≤50 MPa) of brittle mineral particles (e.g., quartz sand) and the pumping mechanical force, and the existing technology lacks low-damage circulation methods.

[0005] The aforementioned problems collectively constrain the resource utilization efficiency of pile foundation slurry: insufficient recovery rate of coarse / medium aggregates, high loss rate of fine components (fine sand, dust), and the crushing index of recycled aggregates is worse than that of natural aggregates due to high micro powder content and poor gradation. How to achieve high-precision separation of wide-particle-size slurry, stable control of swirling under dynamic concentration, and integrity protection of material circulation have become long-standing technical challenges that the industry has been unable to overcome. Summary of the Invention

[0006] One objective of this invention is to provide a method for screening and recycling pile foundation mud, which enables the efficient resource recycling of waste mud from pile foundation engineering, producing recycled aggregates that can replace natural aggregates, and significantly reducing environmental pollution and resource waste.

[0007] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a method for screening and recycling pile foundation mud is provided, comprising the following steps:

[0008] Step 1: Input the pile foundation mud into a high-frequency vibrating screen equipped with an upper 1.8~2.2 mm aperture screen and a lower 0.45~0.55 mm aperture screen to separate coarse aggregate with a particle size greater than 1.8 mm, medium particles with a particle size of 0.45~2.2 mm, and primary mud that passes through the lower screen.

[0009] Step 2: The primary slurry is pressurized to 0.7~1.3 MPa by a centrifugal pump and then pumped into a three-stage series hydrocyclone separation unit; wherein, the underflow port of the first-stage hydrocyclone retains fine sand with a particle size of 0.18~0.52 mm, the underflow port of the second-stage hydrocyclone retains powder particles with a particle size of 0.065~0.22 mm, and the overflow port of the third-stage hydrocyclone outputs ultrafine slurry;

[0010] Step 3: Input the ultrafine slurry into the storage tank and monitor it in real time using online viscosity sensors and online specific gravity sensors.

[0011] When the viscosity of the Martens funnel is in the range of 16~24 s and the specific gravity is in the range of 1.12~1.22 g / cm³ 3 When within the specified range, output regenerated mud;

[0012] When the viscosity value is less than 16 s, add a colloidal reinforcing agent composed of sodium bentonite, nano silica and polyanionic cellulose in a mass ratio of (14~16):(1.8~2.2):1 to the slurry storage tank;

[0013] When the specific gravity is greater than 1.22 g / cm³ 3 At that time, the plate and frame filter press is used to dewater 15% to 35% of the volume of ultrafine slurry in the storage tank, and the filtrate is returned to the storage tank.

[0014] Step 4: Input the coarse aggregate and medium particles obtained in Step 1, the fine sand and powder obtained in Step 2, and the pretreated solid cake produced by the plate and frame filter press in Step 3 into a vertical mixer. Add 2.5%~3.5% aluminate activator and 4%~6% silica fume according to the total mass of solid phase, and mix to form a solid mixture.

[0015] Step 5: The solid mixture is transported to a rotary kiln and calcined at 620~780℃ for 25~35 minutes to generate recycled aggregate.

[0016] Preferably, in step two, dynamic pressure control is performed between the centrifugal pump and the three-stage series cyclone separator; the solid concentration of the primary slurry is detected in real time by an electromagnetic flowmeter, and when the concentration is in the range of 15% to 20%, the output pressure of the centrifugal pump is controlled to 1.1 to 1.3 MPa; when the concentration is in the range of 20% to 25%, the output pressure is controlled to 0.9 to 1.1 MPa; and when the concentration is in the range of 25% to 35%, the output pressure is controlled to 0.7 to 0.9 MPa.

[0017] Preferably, during the dynamic pressure regulation process, the centrifugal pump is subjected to gradual pressure control;

[0018] When a change in solid concentration is detected that triggers a pressure range switching, the centrifugal pump output pressure is controlled to linearly transition to the target pressure range at a rate of 0.1~0.2MPa / s.

[0019] Meanwhile, during the pressure gradual change phase, the fine sand retained at the underflow port of the first-stage hydrocyclone and the powder retained at the underflow port of the second-stage hydrocyclone are combined and introduced into a temporary buffer bin. After the pressure stabilizes to the target range, the material in the temporary buffer bin is re-input into the three-stage series hydrocyclone separation unit for processing.

[0020] Preferably, the reprocessing of materials in the temporary buffer silo is subject to anti-breakage control.

[0021] The material in the temporary buffer bin is pumped back to the three-stage series cyclone separator unit by a screw pump, and the output pressure of the screw pump is controlled at 0.2~0.3 MPa;

[0022] Before material pumping, add silicone oil-based lubricant to the temporary buffer bin at a rate of 0.05% to 0.1% of the total material mass.

[0023] The lubricant and materials are mixed for 1 to 2 minutes using a twin-shaft mixer at a speed of 30 to 50 r / min.

[0024] Preferably, in step four, the solid cake produced by plate and frame filter press in step three is pretreated: the solid cake is fed into a crusher and crushed into particles with a diameter of 1-3 mm; the crushed particles are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content is reduced to 16%-18%; the dried particles, coarse aggregate and medium particles obtained in step one, and fine sand and powder obtained in step two are simultaneously fed into a vertical mixer.

[0025] Preferably, in step four, the moisture content of the coarse aggregate and medium particles obtained in step one, and the fine sand and powder obtained in step two are simultaneously controlled: the coarse aggregate, medium particles, fine sand and powder are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content of the material is reduced to 16%~18%; the dried material and the pretreated solid cake are simultaneously fed into a vertical mixer.

[0026] Preferably, dynamic temperature compensation is performed on the waste heat flue gas input to the perforated drum dryer, including the following steps: a high-temperature buffer tank and a low-temperature buffer tank are connected in parallel at the flue gas outlet of the calcining kiln, with a volume ratio of 1:2 to 1:3, and the output pipes of the high-temperature buffer tank and the low-temperature buffer tank eventually merge into the same main pipe, and are then connected to the perforated drum dryer through a bag filter; the flue gas temperature T at the flue gas outlet of the calcining kiln is monitored in real time by thermocouples.

[0027] When T > 110℃, the high-temperature flue gas treatment path is executed, and the flue gas is introduced into the high-temperature buffer tank for temporary storage for 5~8 min, and then mixed with ambient air at 20~30℃ in its outlet pipe at a volume ratio of flue gas:ambient air = (75~85):(15~25).

[0028] When T < 80℃, the low-temperature flue gas treatment path is executed, and the flue gas is introduced into the low-temperature buffer tank for temporary storage for 3~5 min, and then mixed with the high-temperature flue gas > 110℃ output from the high-temperature buffer tank in its outlet pipe at a volume ratio of flue gas: high-temperature flue gas = (85~90):(10~15).

[0029] When 80℃≤T≤110℃, the direct conveying path is implemented to directly convey the flue gas to the bag filter.

[0030] After mixing, the flue gas is fed into a bag filter. The filter bag is made of PTFE-coated glass fiber with a filtration accuracy of 1 μm. The regenerated slurry from step three is pre-coated on the surface of the filter bag to form a 0.5~1 mm isolation layer. After dust removal, a clean airflow with a temperature of 85~95℃ is output.

[0031] Preferably, a temperature sensor is installed in the clean air chamber of the bag filter to monitor the temperature of the mixed flue gas in real time, and the target temperature range is set to 85℃~95℃.

[0032] When the monitored temperature is higher than 95℃, the mixing ratio of ambient air is automatically increased by 2~3 vol% for every 1℃ increase, while the flue gas output of the high temperature buffer tank is reduced.

[0033] When the monitored temperature is below 85℃, the mixing ratio of high-temperature flue gas is automatically increased. For every 1℃ decrease, the proportion of high-temperature flue gas increases by 1.5~2 vol%, while the flue gas output of the low-temperature buffer tank is reduced.

[0034] Temperature data is collected every 30 seconds. If the temperature deviates from the target value by more than 5°C for three consecutive times, an alarm is triggered and the backup burner is activated to supplement the heat.

[0035] Preferably, a pneumatic regulating valve system is used to perform mixed proportional regulation, controlling the valve position opening change rate within the range of 0.5% / s to 1% / s; wherein, the pneumatic regulating valve system includes four sets of independent valves:

[0036] An ambient air conditioning valve is located at the node where the ambient air duct connects to the high-temperature path mixer.

[0037] High-temperature flue gas branch regulating valve is installed in the branch pipeline from the high-temperature buffer tank to the low-temperature path mixer;

[0038] A low-temperature flue gas output regulating valve is installed on the output pipeline of the low-temperature buffer tank;

[0039] The main output regulating valve of the high-temperature buffer tank is located upstream of the junction of the main output pipeline of the high-temperature buffer tank.

[0040] When the monitored temperature is >95℃: if the system is performing high-temperature path processing, increase the opening of the ambient air regulating valve; if the system is performing low-temperature path processing, decrease the opening of the high-temperature flue gas branch regulating valve; simultaneously decrease the opening of the high-temperature buffer tank main output regulating valve.

[0041] When the monitored temperature is <85℃: if the system is performing low-temperature path processing, increase the opening of the high-temperature flue gas branch regulating valve; increase the opening of the low-temperature flue gas output regulating valve; and simultaneously increase the opening of the high-temperature buffer tank main output regulating valve.

[0042] This invention offers at least the following advantages: Through the synergistic effect of graded screening and multi-stage cyclone separation, it significantly improves the retention efficiency of coarse and medium-sized aggregates, greatly reducing the loss of fine particles; based on the pressure adaptive control mechanism of slurry solid phase concentration, it effectively maintains the stability of the cyclone separation process, avoiding underflow blockage and overflow of coarse particles; the gradual control and buffering strategy during pressure switching significantly reduces the risk of particle breakage and ensures the integrity of material circulation; the introduction of trace lubricants and low-speed mixing significantly suppresses the tendency of fine-grained pulverization during reprocessing; the crushing and waste heat drying of solid cakes significantly improves the uniformity of moisture content in the mixture and enhances the calcination reaction effect; the flue gas temperature dynamic compensation system significantly stabilizes the drying heat source temperature and reduces energy loss; the automatic valve linkage control provides rapid response to temperature fluctuations, ensuring continuous drying; ultimately, it achieves recycled aggregate performance close to that of natural aggregates, realizing the goal of efficient resource utilization and near-zero emissions of slurry solid waste.

[0043] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0044] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0045] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0046] This invention provides a method for screening and recycling pile foundation mud, comprising the following steps:

[0047] Step 1: Input the pile foundation mud into a high-frequency vibrating screen equipped with an upper 1.8~2.2 mm aperture screen and a lower 0.45~0.55 mm aperture screen to separate coarse aggregate with a particle size greater than 1.8 mm, medium particles with a particle size of 0.45~2.2 mm, and primary mud that passes through the lower screen.

[0048] Step 2: The primary slurry is pressurized to 0.7~1.3 MPa by a centrifugal pump and then pumped into a three-stage series hydrocyclone separation unit; wherein, the underflow port of the first-stage hydrocyclone retains fine sand with a particle size of 0.18~0.52 mm, the underflow port of the second-stage hydrocyclone retains powder particles with a particle size of 0.065~0.22 mm, and the overflow port of the third-stage hydrocyclone outputs ultrafine slurry;

[0049] Step 3: Input the ultrafine slurry into the storage tank and monitor it in real time using online viscosity sensors and online specific gravity sensors.

[0050] When the viscosity of the Martens funnel is in the range of 16~24 s and the specific gravity is in the range of 1.12~1.22 g / cm³ 3 When within the specified range, output regenerated mud;

[0051] When the viscosity value is less than 16 s, add a colloidal reinforcing agent composed of sodium bentonite, nano silica and polyanionic cellulose in a mass ratio of (14~16):(1.8~2.2):1 to the slurry storage tank;

[0052] When the specific gravity is greater than 1.22 g / cm³ 3 At that time, the plate and frame filter press is used to dewater 15% to 35% of the volume of ultrafine slurry in the storage tank, and the filtrate is returned to the storage tank.

[0053] Step 4: Input the coarse aggregate and medium particles obtained in Step 1, the fine sand and powder obtained in Step 2, and the pretreated solid cake produced by the plate and frame filter press in Step 3 into a vertical mixer. Add 2.5%~3.5% aluminate activator and 4%~6% silica fume according to the total mass of solid phase, and mix to form a solid mixture.

[0054] Step 5: The solid mixture is transported to a rotary kiln and calcined at 620~780℃ for 25~35 minutes to generate recycled aggregate.

[0055] In this technical solution, the pile foundation slurry is first fed into a high-frequency vibrating screen. This equipment can be configured with an upper screen mesh size of 1.8 mm, 2.0 mm, or 2.2 mm, and a lower screen mesh size of 0.45 mm, 0.50 mm, or 0.55 mm. The vibrating screen can be a dual-motor self-synchronizing vibrator type, and the screen frame material is 304 stainless steel. The separated primary slurry is pressurized by a centrifugal pump, and the pressure can be set to 0.7 MPa, 1.0 MPa, or 1.3 MPa. The pump body flow parts can be made of high-chromium alloy. The pressurized slurry is pumped into a three-stage series hydrocyclone separation unit. The underflow port of the first-stage hydrocyclone retains fine sand with a particle size of 0.18-0.52 mm, the second stage retains powder particles of 0.065-0.22 mm, and the third stage overflow port outputs ultrafine slurry. The hydrocyclone assembly can be a standard hydrocyclone module, and the cylinder material is polyurethane composite material. The ultrafine slurry enters the storage tank. The online viscosity sensor installed inside the tank can be a Marshall funnel electronic timing type, and the specific gravity sensor can be a nuclear density meter.

[0056] The viscosity sensor monitoring thresholds are 16, 20, or 24 seconds, and the specific gravity sensor thresholds are 1.12 g / cm³, 1.18 g / cm³, or 1.22 g / cm³. When the viscosity of the ultrafine slurry falls below 16 s due to excessive dilution, a colloidal reinforcing agent needs to be added to restore its engineering properties. The added colloidal reinforcing agent can be a modified product of drilling-grade calcium-based bentonite (sodium-modified), nano-silica can be precipitated silica, and polyanionic cellulose can be industrial-grade sodium carboxymethyl cellulose. The mass ratio of these three components can be 14:1.8:1, 15:2:1, or 16:2.2:1. When the specific gravity is greater than 1.22 g / cm³, a plate and frame filter press should be used to dewater 20%, 25%, or 30% of the volume of ultrafine slurry in the storage tank. The filter plates for the filter press should ideally be reinforced polypropylene. The solid cake after pressure filtration is mixed with the coarse aggregate (particle size > 1.8 mm), medium particles (particle size 0.45-2.2 mm) obtained by sieving, and the fine sand and powder obtained by cyclone. The added aluminate activator can be the product of CA50 cement clinker grinding, and the silica fume can be metallurgical grade micro silica fume.

[0057] The mixed materials are fed into a vertical mixer, which can be a twin-shaft paddle mixer with paddles made of wear-resistant NM400 steel plate. The solid mixture is then conveyed to a rotary kiln, where the calcination temperature can be set to 620°C, 700°C, or 780°C, and the time can be 25 minutes, 30 minutes, or 35 minutes. The refractory lining of the kiln can be made of high-alumina castable. The recycled aggregate produced through this process has a particle size distribution comparable to that of natural aggregate, with a significantly reduced mud content, enabling the resource utilization of solid components in pile foundation slurry and reducing waste emissions.

[0058] After grading and screening and multi-stage cyclone separation, the pile foundation slurry significantly improves the retention efficiency of coarse and medium-sized aggregates and reduces the loss of fine particles. The ultrafine slurry's performance is ensured to be stable and reliable through real-time viscosity and specific gravity control. Solid components, after being adjusted with colloidal reinforcing agents or dewatered by pressure filtration, are mixed with aluminate activators and silica fume and calcined. The resulting recycled aggregate has low mud content and a reasonable gradation, meeting the requirements for engineering reuse. This method achieves efficient recovery of useful solid phases from the slurry, reduces the need for natural aggregate mining, and minimizes the environmental impact of waste emissions.

[0059] In conventional pile foundation slurry treatment, a single-layer vibrating screen is typically used for screening, with a fixed screen aperture of 1.0 mm. After screening, coarse particles larger than 1.0 mm are retained, while fine particles smaller than 1.0 mm are carried into subsequent processes. The coarse particles on the screen, not graded according to size distribution, are used directly as low-quality aggregate. The slurry passing through the screen is pumped at a fixed pressure of 0.8 MPa into a single-stage hydrocyclone. The hydrocyclone discharges mixed sand particles (0.1-0.5 mm in diameter) from the underflow outlet and wastewater containing fine mud from the overflow outlet. The wastewater after hydrocyclone treatment is then fed into an open-air sedimentation tank for natural settling, requiring at least 48 hours. The sludge at the bottom of the sedimentation tank is excavated and exposed to the open air; when the moisture content drops to 25%-30%, it forms lumpy sludge. The sludge is mixed with the aforementioned coarse particles, and ordinary silicate cement is added as a binder. The mixture is then calcined in a simple sintering furnace at 500-600 degrees Celsius for 40-50 minutes to produce recycled aggregate.

[0060] In existing technologies, the use of single-layer vibrating screens with fixed-aperture screens results in the mixing of medium-sized particles (1.0-2.0 mm) with coarse aggregates, while fine particles smaller than 0.45 mm are completely lost. The hydrocyclone separation stage uses a single-stage hydrocyclone with fixed pump pressure, failing to effectively classify and retain fine sand and powder particles, leading to a mud content exceeding 20% ​​in the underflow product. Mud treatment relies on open-air natural settling, causing viscosity and specific gravity fluctuations to widen to 10-30 seconds and 1.05-1.30 g / cm³, respectively, resulting in uncontrolled recycled mud performance. Furthermore, the lack of moisture content control during solid component mixing, coupled with the direct addition of ordinary silicate cement for calcination, results in recycled aggregates with high mud content and crushing values ​​significantly lower than engineering standards. These defects collectively lead to low useful solid phase recovery rates, making it impossible for recycled aggregates to meet engineering reuse requirements and increasing waste emissions.

[0061] In another technical solution, in step two, dynamic pressure control is performed between the centrifugal pump and the three-stage series cyclone separator; the solid concentration of the primary slurry is detected in real time by an electromagnetic flowmeter. When the concentration is in the range of 15% to 20%, the output pressure of the centrifugal pump is controlled to 1.1 to 1.3 MPa; when the concentration is in the range of 20% to 25%, the output pressure is controlled to 0.9 to 1.1 MPa; and when the concentration is in the range of 25% to 35%, the output pressure is controlled to 0.7 to 0.9 MPa.

[0062] In this technical solution, an electromagnetic flowmeter is installed between the centrifugal pump outlet pipe and the inlet of the three-stage series cyclone separator. This flowmeter can be made of wear-resistant electrode lining material, and the measuring pipe diameter is consistent with the main pipe. The electromagnetic flowmeter detects the solid phase concentration of the primary slurry in real time, and the detection signal is transmitted to the PLC control system. The centrifugal pump can be a variable frequency speed control type, with its motor power matched to the pump head pressure range of 1.0-1.5 MPa. The PLC system has a preset concentration-pressure matching program: when the solid phase concentration is in the range of 15% to 20%, the output control command maintains the centrifugal pump at an outlet pressure of 1.1 to 1.3 MPa; when the concentration is in the range of 20% to 25%, the pressure is adjusted to 0.9 to 1.1 MPa; and when the concentration is in the range of 25% to 35%, the pressure is adjusted to 0.7 to 0.9 MPa.

[0063] The primary slurry flows through an electromagnetic flowmeter, and its solid concentration value is updated every second and input into the PLC system. If the detected concentration is 18% (within the 15%-20% range), the PLC sends a command to the centrifugal pump inverter to increase the pump speed to the corresponding 1.2 MPa output level. If the concentration changes to 22% (entering the 20%-25% range), the PLC controls the inverter to reduce the speed at a rate of 0.5 Hz / second, allowing the pressure to smoothly transition from 1.2 MPa to 1.0 MPa within 15 seconds. When the concentration suddenly increases to 28% (within the 25%-35% range), the PLC immediately initiates a pressure reduction program, controlling the pressure to drop to 0.8 MPa within 20 seconds. Pressure data is fed back to the PLC in real time through the pressure transmitter at the pump outlet, forming a closed-loop control system.

[0064] The electromagnetic flowmeter should be installed at least five times its diameter away from the inlet of the cyclone unit in a straight pipe section to avoid flow field disturbances affecting measurement accuracy. A vector control type frequency converter can be selected for the centrifugal pump to ensure pressure fluctuations are less than ±0.05 MPa. When an abnormal concentration is detected (e.g., exceeding 35% or falling below 15% for 10 consecutive seconds), the PLC automatically switches to safety mode: maintaining a pressure of 0.8 MPa and triggering an audible and visual alarm. A buffer tank with a volume twice the instantaneous flow rate is installed at the inlet pipe of the cyclone unit to absorb water hammer impacts during pressure regulation.

[0065] This dynamic pressure control method effectively avoids hydrocyclone underflow blockage under high-concentration conditions and overflow of coarse particles under low-concentration conditions by matching the slurry solid phase concentration with the hydrocyclone separation pressure requirements in real time. The closed-loop control mechanism maintains a narrow pump pressure fluctuation range, ensuring the particle size classification accuracy of the three-stage hydrocyclone separation unit. Adaptive pressure regulation reduces ineffective work by the centrifugal pump, lowering system energy consumption. Ultimately, it improves the retention efficiency of fine sand and powder particles, providing stable solid raw materials for subsequent resource utilization.

[0066] In conventional pile foundation slurry hydrocyclone separation processes, a centrifugal pump delivers primary slurry to a single-stage hydrocyclone at a fixed pressure of 0.9 MPa. Regardless of variations in the slurry solid concentration (measured range 15%-35%), the pumping pressure remains constant. When the slurry concentration reaches 28%, increased fluid viscosity causes periodic blockage at the hydrocyclone's underflow outlet, requiring manual shutdown for cleaning, each cleaning session taking approximately 15 minutes. When the concentration drops to 16%, insufficient centrifugal force within the hydrocyclone leads to increased loss of the target fine sand (0.1-0.3 mm) from the overflow outlet. The fixed pressure mode also results in energy waste: excessive pumping pressure at low concentrations leads to over 30% of power consumption being wasted, while insufficient pressure at high concentrations necessitates repeated pump start-ups and shutdowns. The overall separation efficiency of the hydrocyclone unit fluctuates by over 25%, and the mud content in the mixed product of fine sand and powder reaches as high as 18%-22%.

[0067] In existing fixed-pressure cyclone separation processes, centrifugal pumps deliver slurry at a constant pressure of 0.9 MPa. When the slurry solid concentration fluctuates to 28%, the high fluid viscosity causes frequent blockages at the underflow port of the hydrocyclone, requiring manual shutdown for cleaning, which takes approximately 15 minutes each time. When the concentration drops to 16%, insufficient centrifugal force causes a large amount of the target fine sand (0.1-0.3 mm in diameter) to be lost from the overflow port. The fixed-pressure mode also leads to significant energy waste: excessive pumping pressure under low-concentration conditions generates ineffective power consumption, while insufficient pressure under high-concentration conditions forces the pump to repeatedly start and stop. Ultimately, this results in the mud content of the fine sand and powder mixture increasing to 18%-22%, and the cyclone separation efficiency fluctuating by more than 25%.

[0068] In another technical solution, during the dynamic pressure regulation process, the centrifugal pump is subjected to gradual pressure control;

[0069] When a change in solid concentration is detected that triggers a pressure range switching, the centrifugal pump output pressure is controlled to linearly transition to the target pressure range at a rate of 0.1~0.2MPa / s.

[0070] Meanwhile, during the pressure gradual change phase, the fine sand retained at the underflow port of the first-stage hydrocyclone and the powder retained at the underflow port of the second-stage hydrocyclone are combined and introduced into a temporary buffer bin. After the pressure stabilizes to the target range, the material in the temporary buffer bin is re-input into the three-stage series hydrocyclone separation unit for processing.

[0071] In this technical solution, the centrifugal pump is equipped with a variable frequency speed-regulating motor, whose speed is precisely controlled by the PLC system through a PID algorithm. When the electromagnetic flowmeter detects a change in solid concentration triggering a pressure range switch (e.g., the concentration rises from 18% to 23%, crossing the 20% threshold), the PLC controls the centrifugal pump to output pressure at a linear rate of 0.1 MPa / s, 0.15 MPa / s, or 0.2 MPa / s to transition to the target pressure range. Specifically, if a pressure reduction from 1.2 MPa to 1.0 MPa (a decrease of 0.2 MPa) is required, the transition takes 20 seconds when the rate is 0.1 MPa / s, and 10 seconds when the rate is 0.2 MPa / s. The pressure transmitter provides real-time feedback of the actual pressure value to the PLC, and automatically compensates for any deviation exceeding ±0.03 MPa.

[0072] During the pressure gradual change phase, the pneumatic three-way valves at the underflow inlets of the first-stage and second-stage hydrocyclones switch synchronously, merging the retained fine sand (0.18-0.52 mm) and powder (0.065-0.22 mm) into a temporary buffer chamber. This buffer chamber can be a vertical conical bottom structure with a volume 2.5 times the minute processing capacity of the hydrocyclone unit, and its inner wall is lined with an ultra-high molecular weight polyethylene wear-resistant layer. A radar level gauge is installed inside the chamber, triggering an audible and visual alarm when the material accumulation height reaches 60% of the chamber capacity. After the pressure stabilizes to the target range (confirmed by a pressure transmitter showing a continuous fluctuation of <±0.02 MPa for 10 seconds), the three-way valve switches back to its original path, and the discharge valve at the bottom of the buffer chamber opens.

[0073] The material in the buffer silo is pumped back to the inlet manifold of the three-stage tandem cyclone separator unit via a screw pump at an output pressure of 0.25 MPa. Before pumping, a silicone oil-based lubricant is added to the buffer silo at a rate of 0.08% of the total material mass, and the mixture is stirred for 90 seconds at a speed of 40 rpm by a twin-shaft paddle mixer installed on the top of the silo. A static mixer is installed at the inlet of the cyclone unit to ensure uniform mixing of the return material with the primary slurry. During reprocessing, the particle size distribution of the underflow product is monitored in real time. If the proportion of particles >0.6 mm in the fine sand exceeds 5%, the mixing time is automatically extended by 30 seconds.

[0074] This pressure gradient control method avoids turbulence and particle mixing in the hydrocyclone field caused by sudden pressure changes by linearly adjusting the pump pressure transition rate. A temporary buffer mechanism completely stores fine sand and powder particles during pressure switching, ensuring continuous material circulation. Silicone oil lubricant and a low-speed mixing process significantly reduce the risk of particle breakage during reprocessing. Ultimately, this achieves a smooth transition in the hydrocyclone separation process, improves the integrity of fine component retention, and provides stable solid raw materials for subsequent resource utilization.

[0075] In traditional hydrocyclone separation processes for pile foundation slurry, when a change in the slurry solids concentration is detected and the centrifugal pump output pressure needs adjustment, the system performs a direct, step-like pressure switch. For example, if the concentration increases and the pressure needs to be reduced, the pump pressure will instantly drop from a high pressure value (e.g., 1.2 MPa) to a target low pressure value (e.g., 0.8 MPa). This sudden pressure change severely disrupts the stable flow field inside the hydrocyclone, causing previously successfully separated coarse particles (e.g., fine sand) and fine particles (e.g., powder) to remix, compromising the classification accuracy. Simultaneously, during the entire unstable period of the pressure switch, the material discharged from the hydrocyclone underflow outlet (i.e., the fine sand and powder that need to be recovered) is not buffered or isolated in any way but continues to be directly fed into subsequent processing steps. This presents two serious problems: First, inside the hydrocyclone where pressure fluctuates wildly, particles (especially brittle minerals such as quartz sand) impact the cyclone wall at high speed under the pressure differential, causing significant physical breakage and resulting in a substantial increase (approximately 15%) in the content of microparticles smaller than 0.1 mm. Second, this material mixed with broken particles directly enters the downstream process, and its quality no longer meets requirements. When these materials, contaminated or broken due to pressure switching, need to be reprocessed, existing technologies typically use high-shear centrifugal pumps to pump them back to the inlet of the hydrocyclone unit. The powerful mechanical shear force generated by the high-speed rotation of the centrifugal pump impeller (linear velocity exceeding 10 m / s) causes secondary damage to the particles, further exacerbating the pulverization phenomenon. The end result is that the proportion of microparticles in the recovered solid material is too high, directly leading to the deterioration of the performance of recycled aggregates produced from these materials, with a compressive strength loss of 8% to 12%. Furthermore, the entire process of pressure step switching and subsequent system stabilization is time-consuming (usually 5 to 8 minutes). During this period, the cyclone separation function is essentially ineffective, and a large amount of target powder particles are lost from the overflow port (loss rate exceeding 30%). A single pressure switching event can cause the overall separation efficiency to drop by more than 25%. In actual engineering, this often leads to problems such as equipment blockage, frequent shutdowns for cleaning (e.g., underflow port blockage rate reaches 40%, cleaning takes about 15 minutes), and the final product (recycled aggregate) having excessive crushing value (>28%, far exceeding the engineering standard of ≤20%), seriously affecting processing efficiency and resource recovery.

[0076] In another technical solution, the reprocessing of materials in the temporary buffer warehouse is subject to anti-breakage control.

[0077] The material in the temporary buffer bin is pumped back to the three-stage series cyclone separator unit by a screw pump, and the output pressure of the screw pump is controlled at 0.2~0.3 MPa;

[0078] Before material pumping, add silicone oil-based lubricant to the temporary buffer bin at a rate of 0.05% to 0.1% of the total material mass.

[0079] The lubricant and materials are mixed for 1 to 2 minutes using a twin-shaft mixer at a speed of 30 to 50 r / min.

[0080] In this technical solution, to reduce the risk of particle breakage during reprocessing of materials in the temporary buffer bin, the following specific measures are taken. When the material is pumped back from the temporary buffer bin to the three-stage cyclone separator, a single screw pump can be used for conveying. The output pressure of this screw pump is set in the lower range of 0.2 MPa to 0.3 MPa, for example, 0.25 MPa. This type of pump can be installed on the bottom outlet pipe of the temporary buffer bin, and its low shear characteristics help protect particle integrity.

[0081] Before pumping the material, a silicone oil-based lubricant needs to be added to the temporary buffer chamber. This lubricant can be an industrial-grade, low-viscosity silicone oil liquid. The amount added should be controlled to be 0.05% to 0.1% of the total mass of the material in the buffer chamber, for example, 0.08%. The lubricant inlet can be located on the top or side wall of the temporary buffer chamber.

[0082] After adding lubricant, start the twin-shaft paddle mixer installed inside the temporary buffer chamber or connected to the chamber body. This mixer operates at a low speed, set between 30 and 50 revolutions per minute (RPM), for example, 40 RPM. The mixing time is controlled between 1 and 2 minutes, for example, 1.5 minutes. This low-speed mixing allows the silicone oil lubricant to be coated more evenly on the surface of the material particles, reducing friction between particles and between particles and the equipment.

[0083] During operation, once the pressure has stabilized within the target range, the operator or automated system first metered and added the prescribed amount of silicone oil-based lubricant to the temporary buffer bin. Next, the twin-shaft mixer was started and run at a set low speed for a specified time to mix the lubricant with the fine sand and powder temporarily stored in the bin. After mixing, the low-pressure screw pump located at the buffer bin outlet was started, and its output pressure was adjusted and maintained between 0.2 MPa and 0.3 MPa (e.g., 0.25 MPa). The mixed material was then smoothly pumped back to the main inlet pipe of the three-stage tandem cyclone separator unit for subsequent re-separation processing.

[0084] This technical solution reduces the mechanical stress on particles during pumping by employing a low-shear screw pump and strictly controlling its low output pressure. Adding an appropriate amount of silicone-based lubricant and mixing at low speed forms a lubricating layer on the particle surface, effectively reducing the friction and collision intensity between particles and between particles and the pipe wall during conveying and recycling. The low-speed mixing process itself also avoids additional impact or extrusion damage to the material. These measures work together to help maintain the original particle size and integrity to the maximum extent during material reprocessing, reducing the generation of fine powder and contributing to the stable performance of subsequent recycled aggregate products.

[0085] In traditional pile foundation slurry treatment processes, when the hydrocyclone system needs to reprocess temporarily stored materials due to pressure adjustments, a high-output-pressure centrifugal pump is commonly used to pump the fine sand and powder materials in the temporary buffer bin back to the hydrocyclone unit. These centrifugal pumps typically operate in a high pressure range, such as 0.8 MPa to 1.0 MPa. During pumping, the high-speed rotating impeller exerts significant mechanical shear forces on the material, easily causing brittle mineral particles to break. Before the material is discharged from the buffer bin for reprocessing, no lubricant is usually added. The particulate material enters the pumping system directly in a dry or slightly moist state, resulting in intense friction and collisions between particles, and between particles and the pump body and pipe walls. Furthermore, if some mixing of the material is required (even without the addition of lubricant), traditional processes often use high-speed mixing equipment, with speeds often set above 100 rpm. This high-speed agitation further exacerbates the impact and wear between material particles.

[0086] In another technical solution, in step four, the solid cake produced by plate and frame filter press in step three is pretreated: the solid cake is fed into a crusher and crushed into particles with a particle size of 1~3 mm; the crushed particles are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content is reduced to 16%~18%; the dried particles, coarse aggregate and medium particles obtained in step one, and fine sand and powder obtained in step two are simultaneously fed into a vertical mixer.

[0087] In this technical solution, when the solid cake-like material is fed into the crusher, a double-roll crusher can be selected. The roller surface material can be high-chromium alloy cast iron, and the roller gap adjustment range can be set to 1-3 mm. The crushed particles are conveyed to a perforated drum dryer. The dryer cylinder can be made of carbon steel lined with 304 stainless steel screen plates, and the screen aperture can be set to 5 mm. The waste heat flue gas duct of the rotary calcining kiln can be equipped with a high-temperature resistant flexible connection, and the interface flange can be a PN16 standard flange. The vertical mixer can be a twin-shaft paddle structure, and the paddles can be made of NM400 wear-resistant steel plate.

[0088] The crusher can be located below the discharge port of the plate and frame filter press, connected via a sealed chute. The inner wall of the chute can be lined with ultra-high molecular weight polyethylene wear-resistant plate. The perforated drum dryer can be installed downstream of the flue gas exhaust duct of the calcining kiln, with an expansion joint installed at the inlet to compensate for thermal displacement. The dryer and the vertical mixer can be connected via a bucket elevator, with the elevator buckets made of engineering plastics. The insulation layer of the flue gas duct can be made of aluminum silicate fiber felt, with a thickness of 80 mm.

[0089] Solid cakes (moisture content approximately 35-40%) discharged from the plate and frame filter press fall into a double-roll crusher via a chute. Operators adjust the roller gap according to the hardness of the cakes: a 3mm gap for clay cakes and a 1mm gap for cakes with high sand content. After crushing, particles with a diameter of 1-3mm are fed into a perforated drum dryer via a vibrating feeder. Simultaneously, waste heat from the rotary kiln (temperature fluctuation range 80-150℃) is introduced into the dryer's inlet via a pipeline. The dryer operates at a speed of 4-6 rpm, with the material residence time controlled at 15-20 minutes, reducing the moisture content to 16-18%. The dried particles are then conveyed by a bucket elevator to the feed inlet of a vertical mixer, where they are simultaneously added to the mixing process along with coarse aggregate and medium particles separated by a high-frequency vibrating screen, as well as fine sand and powder obtained from cyclone separation.

[0090] This technical solution uses crushing to form uniform particles from solid cakes, preventing clumping during subsequent mixing; waste heat flue gas drying reduces the material's moisture content to the target range, improving mixing uniformity; and simultaneous input of various solid components ensures consistent material entry into the mixer. This pretreatment process creates favorable conditions for subsequent mixing and calcination of aluminate activators and silica fume.

[0091] In conventional pile foundation slurry treatment processes, a single-layer vibrating screen is first used for solid-liquid separation, with a fixed screen aperture of 1.0 mm. After screening, coarse particles larger than 1.0 mm are retained, while fine particles smaller than 1.0 mm are carried into subsequent processes. Due to the lack of grading, a large number of medium particles (0.5-1.0 mm) are mixed in with the coarse particles on the screen, while fine particles smaller than 0.45 mm are completely lost. The slurry under the screen is pumped into a single-stage hydrocyclone at a fixed pressure of 0.9 MPa by a centrifugal pump. When the slurry solid concentration fluctuates to 28%, the high viscosity causes frequent blockage of the hydrocyclone's underflow outlet, requiring manual shutdown for cleaning, which takes about 15 minutes each time. When the concentration drops to 16%, the centrifugal force of the cyclone is insufficient, resulting in an increased loss rate of the target fine sand (0.1-0.3 mm) from the overflow outlet. The cyclone separation efficiency fluctuates by more than 25%, and the mud content of the underflow product reaches 22%. The wastewater after vortexing is fed into an open-air sedimentation tank and allowed to settle naturally for over 48 hours, resulting in lumpy sludge with a moisture content of 30% at the bottom. This sludge is directly mixed with screened coarse particles, and ordinary silicate cement is added as a binder. The mixture is then calcined in a simple sintering furnace at 550 degrees Celsius for 45 minutes. The resulting recycled aggregate has a high mud content, a crushing value that is more than 15% lower than that of natural aggregate, and an uneven particle size distribution, failing to meet engineering gradation requirements.

[0092] In another technical solution, in step four, the moisture content of the coarse aggregate and medium particles obtained in step one, and the fine sand and powder obtained in step two are simultaneously controlled: the coarse aggregate, medium particles, fine sand and powder are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content of the material is reduced to 16%~18%; the dried material and the pretreated solid cake are simultaneously fed into a vertical mixer.

[0093] In this technical solution, coarse aggregate, medium-sized particles, fine sand, and powder can be fed into a perforated drum dryer via a belt conveyor. The dryer drum can be made of carbon steel lined with 304 stainless steel sieve plates, with a sieve aperture of 5 mm. The drum inclination angle can be adjusted to 2-5 degrees. The waste heat flue gas duct of the rotary calcining kiln can be connected to the dryer inlet hood via an expansion joint, and the outer wall of the duct can be covered with an 80 mm thick aluminum silicate fiber insulation layer. The dryer outlet can be connected to a bucket elevator via a sealed chute. The elevator can be a chain conveyor, and the buckets can be made of nylon 66. The final dried material and the pretreated solid cake can be simultaneously fed into a twin-shaft paddle vertical mixer.

[0094] Coarse aggregate and medium-sized particles separated by a high-frequency vibrating screen fall onto a belt conveyor via a vibrating feeder. Simultaneously, fine sand and powder retained by the three-stage cyclone separator are fed into the same conveyor belt via a closed screw conveyor. The mixture is continuously fed into the feed end of the perforated drum dryer at a flow rate of 1.5-2 tons / hour. Waste heat flue gas from the rotary kiln is introduced into the dryer via a branch of the main flue, and the flue gas inlet temperature is monitored in real time by thermocouples. The dryer operates at a speed of 4-6 rpm, and lifting plates installed on the inner wall of the drum repeatedly throw the material up, allowing the flue gas to penetrate the material layer. After drying, the material is screened by a grid at the discharge end to remove impurities and then conveyed by a bucket elevator to the feed hopper of a vertical mixer, where it is simultaneously fed into the mixing process along with the crushed and dried solid cake.

[0095] The temperature of the waste heat flue gas entering the dryer is controlled within the range of 85-95℃, and the residence time of the material in the dryer is set to 18-22 minutes. Samples are taken from the dryer outlet every 30 minutes: a 200g sample is placed in a 105℃ oven and dried to constant weight, and the moisture content is calculated. When the measured value is higher than 18%, the residence time is automatically extended to 25 minutes; when the measured value is lower than 16%, the residence time is shortened to 15 minutes. After drying, the material is stored in a moisture-proof chamber, with the humidity maintained below 45%, ensuring that the moisture content is stable within the range of 16-18% when fed into the mixer. By adjusting the dryer speed or using zoned temperature control, materials with different initial moisture contents (D) can simultaneously reach the target value of 16-18%.

[0096] This technical solution achieves coordinated control of the moisture content of multi-component materials through waste heat flue gas drying, avoiding uneven mixing caused by differences in moisture content; a closed conveying system prevents the dried materials from absorbing moisture; and constant temperature control and residence time adjustment ensure stable moisture content meeting standards. This provides the foundation for the subsequent uniform mixing of the solid mixture and the activator.

[0097] In conventional pile foundation mud resource utilization processes, coarse aggregate and medium-sized particles separated by high-frequency vibrating screens are stored in the open air, where the moisture content fluctuates by 8%-30% due to weather conditions. Fine sand and powder separated by cyclone separation require natural drying, which takes 48 hours in summer to reduce the moisture content to below 20%, and over 72 hours in winter. Solid cakes produced by plate and frame filter presses are directly crushed into 5-10 mm particles without drying. When these components are fed into a twin-shaft mixer by a loader, the significant differences in moisture content (8% for coarse aggregate, 22% for fine sand, and 35% for solid cakes) cause the added aluminate activator and silica fume to easily adhere to the surface of the high-moisture materials, forming agglomerates. The mixing process needs to be extended to over 15 minutes, and even then, 10%-15% of the activator remains unevenly dispersed. When the mixed materials are fed into the rotary kiln for calcination, uneven moisture content leads to localized overheating or under-calcination: high-moisture areas require more heat to absorb, extending the calcination time to 40 minutes; low-moisture areas have already sintered at 620℃. In the generated recycled aggregate, 5%-8% of the particles have insufficient strength due to under-calcination, and the crushing value is 12%-18% lower than that of natural aggregate.

[0098] In another technical solution, dynamic temperature compensation is performed on the waste heat flue gas input to the perforated drum dryer, including the following steps: a high-temperature buffer tank and a low-temperature buffer tank are connected in parallel at the flue gas outlet of the calcining kiln, with a volume ratio of 1:2 to 1:3. The output pipes of the high-temperature buffer tank and the low-temperature buffer tank eventually merge into the same main pipe, which is then connected to the perforated drum dryer via a bag filter. The flue gas temperature T at the flue gas outlet of the calcining kiln is monitored in real time using thermocouples.

[0099] When T > 110℃, the high-temperature flue gas treatment path is executed, and the flue gas is introduced into the high-temperature buffer tank for temporary storage for 5~8 min, and then mixed with ambient air at 20~30℃ in its outlet pipe at a volume ratio of flue gas:ambient air = (75~85):(15~25).

[0100] When T < 80℃, the low-temperature flue gas treatment path is executed, and the flue gas is introduced into the low-temperature buffer tank for temporary storage for 3~5 min, and then mixed with the high-temperature flue gas > 110℃ output from the high-temperature buffer tank in its outlet pipe at a volume ratio of flue gas: high-temperature flue gas = (85~90):(10~15).

[0101] When 80℃≤T≤110℃, the direct conveying path is implemented to directly convey the flue gas to the bag filter.

[0102] After mixing, the flue gas is fed into a bag filter. The filter bag is made of PTFE-coated glass fiber with a filtration accuracy of 1 μm. The regenerated slurry from step three is pre-coated on the surface of the filter bag to form a 0.5~1 mm isolation layer. After dust removal, a clean airflow with a temperature of 85~95℃ is output.

[0103] In this technical solution, a K-type armored thermocouple (temperature range 0-400℃) is installed at the flue gas outlet of the calcining kiln to monitor the flue gas temperature T in real time. The main flue gas pipeline is divided into three paths: the first path connects to a high-temperature buffer tank via a DN200 pipeline, which can be a vertical carbon steel storage tank (15 m³ / s). 3 The inner lining is made of 310S stainless steel, and the outer layer is covered with an 80 mm aluminum silicate insulation layer; the second route connects to the cryogenic buffer tank via a DN250 pipe, which can be a horizontal carbon steel tank (30 m³ / s). 3 The first line is lined with 304 stainless steel; the second line is a straight-through pipe (DN300). The output pipes of the high-temperature buffer tank and the low-temperature buffer tank merge into the DN350 main pipe, which connects to the inlet of the perforated drum dryer via a bag filter (the filter bag material is PTFE-coated glass fiber, with a filtration accuracy of 1 μm). A static mixer is installed on the outlet pipe of the high-temperature buffer tank, and the ambient air pipe (DN100) is connected to the upstream of the mixer via a centrifugal fan. A pneumatic regulating valve is installed at the mixing node. A three-way mixer is installed on the outlet pipe of the low-temperature buffer tank, and a branch connects to the output pipe of the high-temperature buffer tank (DN150). A pneumatic butterfly valve is installed at the branch node.

[0104] During operation, when the thermocouple detects T > 110℃ (e.g., 120℃), the pneumatic three-way valve switches to the high-temperature path: the flue gas is introduced into the high-temperature buffer tank and stored for 6 minutes, then mixed with 25℃ ambient air at a volume ratio of 80:20 in the outlet static mixer. When T < 80℃ (e.g., 70℃), the system switches to the low-temperature path: the flue gas is introduced into the low-temperature buffer tank and stored for 4 minutes, then mixed with 115℃ flue gas output from the high-temperature buffer tank at a volume ratio of 88:12 in the outlet three-way mixer. When T is between 80-110℃ (e.g., 95℃), the flue gas passes directly into the bag filter. Before the mixed flue gas enters the bag filter, the regenerated slurry from step three (specific gravity 1.18 g / cm³) is pumped through a slurry pump. 3 The filter bag is sprayed in a circulating manner to form a 0.8 mm isolation layer; after dust removal, a 90℃ clean airflow is output to the dryer.

[0105] A Pt100 temperature sensor is installed in the clean air chamber of the bag filter, with a target temperature set at 90℃ (allowable deviation ±5℃). If the monitored temperature reaches 97℃ (>95℃), the PLC controls the ambient air regulating valve to increase its opening by 5% (calculated at 2.5 vol% for every 1℃ above the target temperature), and simultaneously reduces the opening of the main output valve of the high-temperature buffer tank by 10%. If the temperature drops to 83℃ (<85℃), the high-temperature flue gas branch regulating valve opening is increased by 7% (calculated at 1.8 vol% for every 1℃ below the target temperature), and simultaneously increases the opening of the low-temperature flue gas output valve by 8%. Temperature data is collected every 30 seconds; if the temperature is detected to be ≤85℃ or ≥95℃ three times consecutively (e.g., 84℃, 83℃, 82℃), an audible and visual alarm is triggered, and the natural gas backup burner is activated to supplement heat.

[0106] This technical solution stabilizes fluctuating flue gas (70-150℃) to a drying heat source of 85-95℃ through staged temporary storage in dual buffer tanks and adjustment of mixing ratios. A pre-coated recycled slurry isolation layer on the filter bags effectively intercepts fine dust, reducing filter bag clogging. Automatic valves respond to temperature fluctuations, ensuring continuous operation of the drying process. Ultimately, this improves waste heat utilization, reduces drying energy consumption, and extends the service life of the filter bags.

[0107] In traditional pile foundation slurry resource utilization processes, waste heat flue gas from the calcining kiln is directly fed into a perforated drum dryer to dry solid materials. Due to fluctuations in the calcining kiln's operating conditions (such as changes in feed rate and fuel calorific value), the flue gas outlet temperature fluctuates drastically, with measured temperatures ranging from 80℃ to 150℃. When high-temperature flue gas (>110℃) directly enters the dryer, the material inside the drum hardens and forms a crust due to localized overheating, preventing effective evaporation of internal moisture. This results in uneven moisture content distribution in the dried material (some areas <10%, some areas >25%). Simultaneously, the high-temperature flue gas accelerates the deformation and cracking of the dryer's screen plates, increasing maintenance frequency. When low-temperature flue gas (<80℃) is input, drying efficiency drops sharply, and the material moisture content cannot be reduced to below 20%, necessitating the use of an electric heater for auxiliary heating, increasing energy costs by more than 30%.

[0108] Dust in the flue gas (mainly alumina powder) enters the dryer directly without pretreatment, forming an ash coating layer (3%-5%) on the material surface, degrading the purity of recycled aggregate. To mitigate temperature fluctuations, some projects use simple buffer tanks to temporarily store the flue gas, but the single-tank structure cannot provide graded control: during high-temperature periods, cooling can only be achieved by manually mixing in cold air, requiring operators to continuously monitor the thermometer and manually adjust valves, with a response lag of more than 5 minutes; during low-temperature periods, external burners are required for supplemental heating, but the uneven mixing of flue gas and flame during the supplemental heating process causes local overheating (>200℃), burning the ordinary fiberglass filter bags of the downstream bag filter (replaced an average of 12 times per year). The dust collector lacks a pre-coating layer, allowing fine dust (particle size <5μm) to penetrate the filter bags and enter the drying system, contaminating the material and causing filter bag caking and failure, resulting in abnormal fluctuations in system negative pressure up to ±500Pa. The final drying heat source temperature ran out of control (60℃-130℃), resulting in excessive moisture content (>20%) and high impurity content in the recycled aggregate, increased energy consumption in the calcination process and a product qualification rate of less than 70%.

[0109] In another technical solution, a temperature sensor is installed in the clean air chamber of the bag filter to monitor the temperature of the mixed flue gas in real time, and the target temperature range is set to 85℃~95℃.

[0110] When the monitored temperature is higher than 95℃, the mixing ratio of ambient air is automatically increased by 2~3 vol% for every 1℃ increase, while the flue gas output of the high temperature buffer tank is reduced.

[0111] When the monitored temperature is below 85℃, the mixing ratio of high-temperature flue gas is automatically increased. For every 1℃ decrease, the proportion of high-temperature flue gas increases by 1.5~2 vol%, while the flue gas output of the low-temperature buffer tank is reduced.

[0112] Temperature data is collected every 30 seconds. If the temperature deviates from the target value by more than 5°C for three consecutive times, an alarm is triggered and the backup burner is activated to supplement the heat.

[0113] In this technical solution, the real-time temperature monitoring device installed in the clean air chamber of the bag filter can be a Pt100 resistance temperature sensor. This sensor is installed in the middle section of the airflow channel at the center of the clean air chamber, avoiding the turbulence area on the pipe wall. The alarm device can be an audible and visual alarm, installed on the central control cabinet panel; the backup heat source compensation device can be a natural gas burner, installed in the bypass of the main air inlet pipe of the bag filter, and connected to the main pipe through a flange. The data acquisition module is integrated into the PLC control system, with a sampling period set to 30 seconds / time, and the control signal transmission uses a 4-20mA current loop.

[0114] The temperature sensor is set to a target range of 85℃ to 95℃, and the monitoring data is updated every 30 seconds. When the detected temperature is higher than 95℃ (e.g., 97℃), the system automatically adjusts the ambient air mixing ratio: increasing the ambient air by 2.5 vol% for every 1℃ increase (e.g., increasing by 5 vol% for every 2℃ increase), and simultaneously reducing the opening of the main output regulating valve of the high-temperature buffer tank by 10%. When the detected temperature is lower than 85℃ (e.g., 83℃), increasing the high-temperature flue gas by 1.75 vol% for every 1℃ decrease (e.g., increasing by 3.5 vol% for every 2℃ decrease), and simultaneously reducing the opening of the low-temperature buffer tank output regulating valve by 8%. If the detected temperature deviates from the target value for three consecutive times (e.g., three consecutive detected values ​​of 100℃, 101℃, 102℃ or 80℃, 79℃, 78℃), an audible and visual alarm is triggered, and the backup natural gas burner is started. The burner's output heat is increased by 5% of the rated power for every 1℃ deviation.

[0115] Real-time temperature monitoring and dynamic proportional adjustment maintain the flue gas temperature within the set range, ensuring the stability of the drying heat source; the alarm mechanism and backup heat source respond in conjunction to avoid drying interruption due to abnormal temperature; closed-loop control reduces the need for manual intervention and ensures the reliability of continuous system operation.

[0116] In existing pile foundation slurry resource utilization processes, waste heat flue gas from the calcining kiln is directly fed into a perforated drum dryer to dry solid materials. Due to fluctuations in the kiln feed rate and differences in fuel calorific value, the flue gas temperature varies drastically, with measured outlet temperatures ranging from 80℃ to 150℃. When high-temperature flue gas exceeding 110℃ directly enters the dryer, the material surface rapidly hardens and forms a crust due to localized overheating, preventing effective evaporation of internal moisture. This results in severely uneven moisture content distribution in the dried material, with some areas below 10% and others above 25%. Simultaneously, the high temperature accelerates thermal deformation and cracking of the dryer's screen plates, significantly increasing equipment maintenance frequency. When low-temperature flue gas below 80℃ is input, drying efficiency drops sharply, and the material moisture content cannot be reduced to below 20%, necessitating the use of electric heaters for auxiliary heating, increasing additional energy costs by over 30%. Furthermore, dust such as alumina powder carried in the flue gas comes into direct contact with the material without pretreatment, forming a 3% to 5% ash coating layer on the particle surface, degrading the purity of the recycled aggregate.

[0117] To mitigate temperature fluctuations, some projects employed a simple single-tank buffer structure to temporarily store flue gas. However, this approach had fundamental flaws: during high-temperature periods, operators relied solely on manual observation of thermometers and adjustment of cold air valves, resulting in a response lag of over 5 minutes. During this time, the high-temperature flue gas caused material crusting. During low-temperature periods, external burners were required to supplement heat, but uneven mixing of flue gas and flames led to localized overheating exceeding 200°C, frequently burning out the ordinary fiberglass filter bags in downstream baghouse dust collectors, requiring replacement an average of 12 times per year. The dust collection system lacked a pre-coating process, allowing fine dust particles smaller than 5 micrometers to penetrate the filter bags and enter the dryer, contaminating the material and causing filter bag caking and failure. Abnormal negative pressure fluctuations in the system reached ±500 Pa. The entire drying process lacked real-time temperature feedback and automatic compensation mechanisms; operators could only estimate adjustments based on experience, failing to accurately match dynamic demands. Ultimately, the drying heat source temperature spiraled out of control between 60°C and 130°C, resulting in recycled aggregate moisture content exceeding the standard by over 20%, increased impurity content, increased energy consumption in the calcination process, and a product qualification rate of less than 70%.

[0118] In another technical solution, a pneumatic regulating valve system is used to perform mixed proportional regulation, controlling the valve opening change rate within the range of 0.5% / s to 1% / s; wherein, the pneumatic regulating valve system includes four sets of independent valves:

[0119] An ambient air conditioning valve is located at the node where the ambient air duct connects to the high-temperature path mixer.

[0120] High-temperature flue gas branch regulating valve is installed in the branch pipeline from the high-temperature buffer tank to the low-temperature path mixer;

[0121] A low-temperature flue gas output regulating valve is installed on the output pipeline of the low-temperature buffer tank;

[0122] The main output regulating valve of the high-temperature buffer tank is located upstream of the junction of the main output pipeline of the high-temperature buffer tank.

[0123] When the monitored temperature is >95℃: if the system is performing high-temperature path processing, increase the opening of the ambient air regulating valve; if the system is performing low-temperature path processing, decrease the opening of the high-temperature flue gas branch regulating valve; simultaneously decrease the opening of the high-temperature buffer tank main output regulating valve.

[0124] When the monitored temperature is <85℃: if the system is performing low-temperature path processing, increase the opening of the high-temperature flue gas branch regulating valve; increase the opening of the low-temperature flue gas output regulating valve; and simultaneously increase the opening of the high-temperature buffer tank main output regulating valve.

[0125] In this technical solution, the ambient air regulating valve in the pneumatic regulating valve system can be a butterfly valve, installed at the flange interface where the ambient air pipeline connects to the high-temperature path static mixer. The high-temperature flue gas branch regulating valve can be a ball valve, installed in the middle section of the branch pipeline from the high-temperature buffer tank to the low-temperature path three-way mixer. The low-temperature flue gas output regulating valve can be a plug valve, located 1.5 meters from the tank body on the outlet pipeline of the low-temperature buffer tank. The high-temperature buffer tank main output regulating valve can be a gate valve, installed on the straight pipe section before the high-temperature buffer tank main output pipeline merges into the main pipeline, 2 meters upstream of the merging point. The valve actuator can be a cylinder-driven type, with the air source pressure set to 0.6 MPa.

[0126] The valve body can be made of 304 stainless steel, and the sealing material can be graphite-filled PTFE. The valve opening rate is controlled by PLC programming and set to 0.75% / second (within the range of 0.5-1% / second). A Pt100 platinum resistance temperature sensor can be used, installed on the central axis of the clean air chamber of the bag filter, with a temperature response time of less than 3 seconds. When the monitored temperature is higher than 95℃ (e.g., 97℃), the PLC calculates the opening increment by increasing the proportion of ambient air by 2.5% for every 1℃ increase; when the monitored temperature is lower than 85℃ (e.g., 83℃), the opening increment is calculated by increasing the proportion of high-temperature flue gas by 1.8% for every 1℃ decrease.

[0127] During operation, when the temperature sensor in the clean air chamber of the bag filter detects 97℃ (target range 85-95℃), the PLC determines the current system operating path: if it is in a high-temperature path processing state (i.e., flue gas mixes with ambient air via a high-temperature buffer tank), the opening of the ambient air regulating valve is increased by 5%, and the opening of the main output regulating valve of the high-temperature buffer tank is simultaneously decreased by 8%; if it is in a low-temperature path processing state (i.e., flue gas mixes with high-temperature flue gas via a low-temperature buffer tank), the opening of the high-temperature flue gas branch regulating valve is decreased by 6%. The valve opening is linearly adjusted at a rate of 0.75% / second, completing the action within 20 seconds. After adjustment, the flue gas temperature drops to 93℃, returning to the target range. This system responds to temperature fluctuations through multi-valve linkage, maintaining the stability of the drying heat source temperature, avoiding material crusting due to overheating or a decrease in drying efficiency caused by low temperatures, and ensuring the uniformity of the moisture content of the recycled aggregate.

[0128] In traditional pile foundation slurry recycling processes, waste heat flue gas from the calcining kiln is directly fed into a perforated drum dryer to dry solid materials. Due to fluctuations in the kiln feed rate and differences in fuel calorific value, the flue gas temperature varies drastically, with measured outlet temperatures ranging from 80℃ to 150℃. When high-temperature flue gas exceeding 110℃ directly enters the dryer, the material surface rapidly hardens and forms a crust due to localized overheating, preventing effective evaporation of internal moisture. This results in severely uneven moisture content distribution after drying, with some areas below 10% and others above 25%. Simultaneously, the high temperature accelerates thermal deformation and cracking of the dryer's screen plates, significantly increasing equipment maintenance frequency. When low-temperature flue gas below 80℃ is input, drying efficiency drops sharply, and the material moisture content cannot be reduced to below 20%, necessitating the use of electric heaters for auxiliary heating, increasing additional energy costs by over 30%. Furthermore, dust such as alumina powder carried in the flue gas comes into direct contact with the material without pretreatment, forming a 3% to 5% ash coating on the particle surface, degrading the purity of the recycled aggregate.

[0129] To mitigate temperature fluctuations, some projects employed a simple single-tank buffer structure to temporarily store flue gas. However, this approach had fundamental flaws: during high-temperature periods, operators relied solely on manual observation of thermometers and adjustment of cold air valves, resulting in a response lag of over 5 minutes. During this time, the high-temperature flue gas caused material crusting. During low-temperature periods, external burners were required to supplement heat, but uneven mixing of flue gas and flames led to localized overheating exceeding 200°C, frequently burning out the ordinary fiberglass filter bags in downstream baghouse dust collectors, requiring replacement an average of 12 times per year. The dust collection system lacked a pre-coating process, allowing fine dust particles smaller than 5 micrometers to penetrate the filter bags and enter the dryer, contaminating the material and causing filter bag caking and failure. Abnormal negative pressure fluctuations in the system reached ±500 Pa. The entire drying process lacked real-time temperature feedback and automatic compensation mechanisms; operators could only estimate adjustments based on experience, failing to accurately match dynamic demands. Ultimately, the drying heat source temperature spiraled out of control between 60°C and 130°C, resulting in recycled aggregate moisture content exceeding the standard by over 20%, increased impurity content, increased energy consumption in the calcination process, and a product qualification rate of less than 70%.

[0130] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A method for screening and recycling pile foundation mud, characterized in that, Includes the following steps: Step 1: Input the pile foundation mud into a high-frequency vibrating screen equipped with an upper 1.8~2.2 mm aperture screen and a lower 0.45~0.55 mm aperture screen to separate coarse aggregate with a particle size greater than 1.8 mm, medium particles with a particle size of 0.45~2.2 mm, and primary mud that passes through the lower screen. Step 2: The primary slurry is pressurized to 0.7~1.3 MPa by a centrifugal pump and then pumped into a three-stage series hydrocyclone separation unit; wherein, the underflow port of the first-stage hydrocyclone retains fine sand with a particle size of 0.18~0.52 mm, the underflow port of the second-stage hydrocyclone retains powder particles with a particle size of 0.065~0.22 mm, and the overflow port of the third-stage hydrocyclone outputs ultrafine slurry; The centrifugal pump and the three-stage cyclone separator unit are subject to dynamic pressure control. The solid concentration of the primary slurry is monitored in real time using an electromagnetic flowmeter. When the concentration is in the range of 15% to 20%, the output pressure of the centrifugal pump is controlled to 1.1 to 1.3 MPa; when the concentration is in the range of 20% to 25%, the output pressure is controlled to 0.9 to 1.1 MPa; and when the concentration is in the range of 25% to 35%, the output pressure is controlled to 0.7 to 0.9 MPa. During the dynamic pressure control process, the centrifugal pump is subjected to gradual pressure control. When a change in solid concentration is detected that triggers a pressure range switching, the centrifugal pump output pressure is controlled to linearly transition to the target pressure range at a rate of 0.1~0.2 MPa / s. Meanwhile, during the pressure gradual change stage, the fine sand intercepted at the underflow port of the first-stage hydrocyclone and the powder intercepted at the underflow port of the second-stage hydrocyclone are combined and introduced into the temporary buffer bin. After the pressure stabilizes to the target range, the material in the temporary buffer bin is re-input into the three-stage series hydrocyclone separation unit for processing. Before the material is pumped, silicone oil-based lubricant is added to the temporary buffer bin. Step 3: Input the ultrafine slurry into the storage tank and monitor it in real time using online viscosity sensors and online specific gravity sensors. When the viscosity of the Martens funnel is in the range of 16~24 s and the specific gravity is in the range of 1.12~1.22 g / cm³ 3 When within the specified range, output regenerated mud; When the viscosity value is less than 16 s, add a colloidal reinforcing agent composed of sodium bentonite, nano silica and polyanionic cellulose in a mass ratio of (14~16):(1.8~2.2):1 to the slurry storage tank; When the specific gravity is greater than 1.22 g / cm³ 3 At that time, the plate and frame filter press is used to dewater 15% to 35% of the volume of ultrafine slurry in the storage tank, and the filtrate is returned to the storage tank. Step 4: Input the coarse aggregate and medium particles obtained in Step 1, the fine sand and powder obtained in Step 2, and the pretreated solid cake produced by the plate and frame filter press in Step 3 into a vertical mixer. Add 2.5%~3.5% aluminate activator and 4%~6% silica fume according to the total mass of solid phase, and mix to form a solid mixture. Step 5: The solid mixture is transported to a rotary kiln and calcined at 620~780℃ for 25~35 minutes to generate recycled aggregate.

2. The method for screening and recycling pile foundation mud as described in claim 1, characterized in that, The reprocessing of materials in the temporary buffer warehouse is subject to anti-breakage control. The material in the temporary buffer bin is pumped back to the three-stage series cyclone separator unit by a screw pump, and the output pressure of the screw pump is controlled at 0.2~0.3 MPa; Before material pumping, add silicone oil-based lubricant to the temporary buffer bin at a rate of 0.05% to 0.1% of the total material mass. The lubricant and materials are mixed for 1 to 2 minutes using a twin-shaft mixer at a speed of 30 to 50 r / min.

3. The method for screening and recycling pile foundation mud as described in claim 1, characterized in that, In step four, the solid cake produced by plate and frame filter press in step three is pretreated: the solid cake is fed into a crusher and crushed into particles with a diameter of 1-3 mm; the crushed particles are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content is reduced to 16%-18%; the dried particles, coarse aggregate and medium particles obtained in step one, and fine sand and powder obtained in step two are simultaneously fed into a vertical mixer.

4. The method for screening and recycling pile foundation mud as described in claim 3, characterized in that, In step four, the moisture content of the coarse aggregate and medium particles obtained in step one, and the fine sand and powder obtained in step two are simultaneously controlled: the coarse aggregate, medium particles, fine sand and powder are fed into a perforated drum dryer and dried using the waste heat flue gas discharged from the rotary kiln in step five, so that the moisture content of the material is reduced to 16%~18%; the dried material and the pretreated solid cake are simultaneously fed into a vertical mixer.

5. The method for screening and recycling pile foundation mud as described in claim 4, characterized in that, Dynamic temperature compensation is applied to the waste heat flue gas input to the perforated drum dryer, including the following steps: A high-temperature buffer tank and a low-temperature buffer tank are connected in parallel at the flue gas outlet of the calcining kiln, with a volume ratio of 1:2 to 1:

3. The output pipes of the high-temperature buffer tank and the low-temperature buffer tank eventually merge into the same main pipe, which is then connected to the perforated drum dryer via a bag filter. The flue gas temperature T at the flue gas outlet of the calcining kiln is monitored in real time using thermocouples. When T > 110℃, the high-temperature flue gas treatment path is executed, and the flue gas is introduced into the high-temperature buffer tank for temporary storage for 5~8 min, and then mixed with ambient air at 20~30℃ in its outlet pipe at a volume ratio of flue gas:ambient air = (75~85):(15~25). When T < 80℃, the low-temperature flue gas treatment path is executed, and the flue gas is introduced into the low-temperature buffer tank for temporary storage for 3~5 min, and then mixed with the high-temperature flue gas output from the high-temperature buffer tank at >110℃ in its outlet pipe at a volume ratio of flue gas: high-temperature flue gas = (85~90):(10~15). When 80℃≤T≤110℃, the direct conveying path is implemented to directly convey the flue gas to the bag filter. After mixing, the flue gas is fed into a bag filter. The filter bag is made of PTFE-coated glass fiber with a filtration accuracy of 1 μm. The regenerated slurry from step three is pre-coated on the surface of the filter bag to form a 0.5~1 mm isolation layer. After dust removal, a clean airflow with a temperature of 85~95℃ is output.

6. The method for screening and recycling pile foundation mud as described in claim 5, characterized in that, The clean air chamber of the bag filter is equipped with a temperature sensor to monitor the temperature of the mixed flue gas in real time, and the target temperature range is set to 85℃~95℃. When the monitored temperature is higher than 95℃, the mixing ratio of ambient air is automatically increased by 2~3 vol% for every 1℃ increase, while the flue gas output of the high temperature buffer tank is reduced. When the monitored temperature is below 85℃, the mixing ratio of high-temperature flue gas is automatically increased. For every 1℃ decrease, the proportion of high-temperature flue gas increases by 1.5~2 vol%, while the flue gas output of the low-temperature buffer tank is reduced. Temperature data is collected every 30 seconds. If the temperature deviates from the target value by more than 5°C for three consecutive times, an alarm is triggered and the backup burner is activated to supplement the heat.

7. The method for screening and recycling pile foundation mud as described in claim 6, characterized in that, A pneumatic control valve system is used to perform mixed proportional regulation, controlling the valve opening change rate within the range of 0.5% / s to 1% / s; the pneumatic control valve system includes four sets of independent valves: An ambient air conditioning valve is located at the node where the ambient air duct connects to the high-temperature path mixer. High-temperature flue gas branch regulating valve is installed in the branch pipeline from the high-temperature buffer tank to the low-temperature path mixer; A low-temperature flue gas output regulating valve is installed on the output pipeline of the low-temperature buffer tank; The main output regulating valve of the high-temperature buffer tank is located upstream of the junction of the main output pipeline of the high-temperature buffer tank. When the monitored temperature is >95℃: if the system is performing high-temperature path processing, increase the opening of the ambient air regulating valve; if the system is performing low-temperature path processing, decrease the opening of the high-temperature flue gas branch regulating valve; simultaneously decrease the opening of the high-temperature buffer tank main output regulating valve. When the monitored temperature is <85℃: if the system is performing low-temperature path processing, increase the opening of the high-temperature flue gas branch regulating valve; increase the opening of the low-temperature flue gas output regulating valve; and simultaneously increase the opening of the high-temperature buffer tank main output regulating valve.